Now that we've looked at the role of the angled brechface in controlled feed... anybody wanna take a crack at the secondary but just as important function of that angle?
No. Not to compensate for the in-battery barrel tilt.
On your mark! Get set! Scratch heads!
Without peeking at the previous week's lesson, did the whole controlled feed, "anti-pop-up" discussion also mention holding the rim still to ensure proper extractor hook engagement?
WAG:
When in lockup, the rim on the brass is held snug between the Brechface and the extractor. When cycled, the barrel drops, pulling the spent Brass down a wee bit. The angled brechface gives a little bit of freeplay on the rim allowing the Brass to flip out and not stovepipe.
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You already did the controlled feed thing, so it can't be anything on the
feed side of the cycle. That leaves the eject side of things. The barrel
drops, and the angle of the brechface does change the relative distance
between the ejector and the brechface. (open the "grip" on the brass rim) Why
else give the brass a bit of wiggleroom if not to aid ejection?
Daaaaaaang! You're good!
It's an aid to primary extraction and quick barrel drop.
Ordnance-spec pistols start to drop the barrel at about .100 or so of slide movement. The case is against the breechface... pretty solidly... until extraction starts, because of residual gas pressure in the barrel. (Nothing moves instantly... not even gas... and neither does pressure fall to zip instantly.) Primary extraction is effected partly by that drop, just as, or just before the hook squarely engages the rim.
As the barrel links down and falls through a short arc and away from the breechface, the angle forms a slight gap below the mid-point of the case rim... which increases with further barrel drop until the breechface is only in contact with the case at the top... the same way it was during feed... which reduces friction and allows a free barrel drop. Were it not for this angle, the case would drag on the barrel and slow its drop to the bed. Upper lug corners would be rounded and slide and barrel lugs would be damaged in pretty short order.
Much as I hold you guys in awe (truly), I'm quite skeptical about the angled breech face being much of a help in either feeding or extraction. The angle is so small, just 52'. If the barrel drops .080 from lockup to barrel bed, an angle of 52' gives about 1.2 thou extra clearance.
And during feeding, the round pops up about .320 from in-the-mag to in-the- chamber (barrel on the bed). In this rise, the forward angle of the breech face gives only 5 thou of overhang.
I can't see these particular small differences as important. Is the angled breech even implemented? It would be nice to see some measurements on what different manufacturers do with this.
Experiments were mentioned in the previous thread, which showed that "The angle can be 89 degrees, 20 minutes... but not 89 degrees, 7 minutes". In another words, that the breech face can be angled less, but not more. I'd like to hear more about these experiments.
Study on it for awhile, and it'll start comin' to ya. No... it doesn't provide much push OR clearance... but it's not really about clearance. It's about getting the pressure off, and sometimes a little is a lot. What's that they say... "A miss is as good as a mile."
The added (downward) push during feeding is an aid to controlled feed that works with all other aspects of that function. Insurance...
A point to consider...
Machining that precise angle takes expensive tooling... the jig/fixture... Extra set-up time for the machinist... extra time spent in gauging the slide for the correct angle... and more rejected slides due to failing the gauge check. In a high-volume contract production, that means money. If it had been deemed unimportant, it would have long been eliminated in the blueprints for the sake of speed and bottom-line profit.
Going by the high number of 1911-pattern pistols that have been turning up with maddening feed/RTB issues these days, I suspect that a large percentage of slides that are out-of-spec on that breechface have slipped through the QA cracks.
The drawing contained in Eric A. Nicolaus' prints clearly shows the angle of the breechface being 89 degrees and 08 seconds as well as the firing pin tunnel at 90 degrees to the the breechface angle. These prints are Dept. of the Army, Springfield Armory documents and are dated 11 Mar 60. There are other dates and changes starting in 1908 and include changes in 1915, 1921, 1964, 1967, 1968 and 1973. I am sure there is a legit reason or reasons for the angle.
Isn't the breechface perpendicular to the barrel when the barrel is in battery?
Not to detract from the theorized benefits of an angled breechface, but JMB may have had simpler reasons.
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Isn't the breechface perpendicular to the barrel when the barrel is in
battery?
Yep, and the reasons were manifold. The angle of the barrel in battery doesn't match the precisely dimensioned 89 degrees/8 minutes, and largely because it doesn't have to, due to the tolerances and clearances of the chambered cartridge. Unnecessary during ignition too, because the brass is malleable enough to "fill in the gap" under pressure.
While the pistol will function quite well with the breechface at 90 degrees... the dead-nuts reliability so often seen in the pistols that adhered closely to print specs is often lacking. When all is "right" we have the examples that never seem to fail... ever... and on the ones that aren't, we see the examples that are "good enough" for gub'mint work... but still have intermittent failures and related stoppages.
I have an early 1991A1 Colt that's been in hard service since I bought it. After 15 years... three barrels... and one complete rebuild/refitting, the gun has never failed to feed/extract/eject, and only occasionally failed to lock the slide on empty... which is a magazine issue. 75,000 rounds on the original extractor, which was replaced during the overhaul as a matter of course, not because it had given a problem... and it had never required retensioning. It's been delegated to the range kit as an emergency spare.
Another one that's a twin to the first will celebrate its 15-year run in the spring...has had maybe a dozen feed/extraction/ejection related malfunctions with pretty much an identical service history. The two pistols have a collective round count of something approaching 275,000 rounds. Both slides checked dead on the money at 89 degrees/8 minutes.
A NRM Colt gave problems early on, including one broken extractor and two that required retensioning periodically. The gun was extremely reliable, and... once it was well-tweaked and fine-tuned... only produces a failure to function about once in 1,000 rounds on average. The breechface on that one is spot on at 90 degrees. All else is within spec on all three pistols.
A fourth beater is a mid-90s production ORM 91A1 that produces the occasional failure to return to battery when hot and dirty. The angle on that breechface is a little removed from print spec at about 89 degrees/30 minutes. Let it cool off, and the failures cease. Start with a clean pistol and let it cool between sets, and it never fails for up to 1,000 rounds in a single day.
The old beaters... the first two that I mentioned... have gone for as much as 5,000 rounds over the course of a week... without cleaning... without a failure of any sort.
Is there a practical difference when reliability is 1,000 rounds good? Probably not. Do I feel better when carrying a gun that passes 5,000 rounds without a failure to function, as opposed to one that will only make it to a thousand? You betcha. Guess which one will be on my hip when the chips are down...
Looks like on the drawing mentioned earlier that the barrel is at an angle of 24 seconds from horizontal with the slide rails when in battery. This figure makes me wonder about the present day examples I'm seeing. Also looks like the slide lugs are speced at an angle of 52 seconds from horizontal. I am not at all familiar with machine shop prints and symbols, so you may assume I am in error.
Oh, I've studied on it, and what's coming to me is that if the barrel starts out parallel to the slide when it's in the barrel bore, and then the lugs lock upwards with 50 thou engagement, and the middle lug is at about 3.4" from the pivot point somewhere in the bushing, that the barrel is now at an angle of about 51'. (InvTan (.050/3.4))= about 50.5'
It's also coming to me that they wanted the breech perpendicular to this bore axis which is angled at about 51' (of course I'm using rough numbers). This would help ease unlocking to some extent (especially if it came a bit early), as was said. This seems like a good idea.
And I don't see how it could *hurt* extraction for this angle to be present, and it might help. But the help-with-feeding stuff seems quite speculative.
Hard to say about this stuff, unless we find pistols that have the angle, and pistols that don't, and see how they do.
Or if the experiments that were mentioned (which were quoted as giving the result that more angling was bad, and less was ok) turn out to be solid.
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But the help-with-feeding stuff seems quite speculative.
Consider for a few minutes what "Controlled Feed" really means, and what is required... and it'll become less speculative... both as to why that precise angle is important, and why mirror-polishing a feed ramp can be detrimental to positive control.
The point is that I do have the pistols with and without the correct angle... and the ones with the correct angle behave like that Energizer Rabbit... while the ones that are at 90 degrees act more like a Ford pickup truck with 100,000 miles on it. Reliable enough for the daily commute... but not really trustworthy for a California Turnaround.
Witness the number of unaltered/untuned USGI 1911/1911A1s and a 1925 commercial Colt in my stable that can't tell the difference between hardball and hollowpoints... and even 200-grain lead SWCs fed from the old "Hardball" magazines. They chug along happily ignorant of the fact that they're only feed reliable with hardball. Open invitation. If you're ever in my neck of the woods, come watch it happen.
So whats the differece in set up 1 to 2 degree that todays companys cannot follow this. Seems so important to reliability. And are they out there?
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Seems so important to reliability. And are they out there?
Oh yeah. But with just a few minutes of angle, all it takes is for a jig or fixture to slip a tiny bit... or a small machining chip... or even a piece of that strip of paper so near and dear to a machinist's heart in the works to throw it off... and apparently, there's not a lot of careful gauging in effect during the final assembly... so a few more than a few slip through the cracks.
I've often said that reliable function with the 1911 is usually dependent on a good magazine... a good extractor... and decent ammo, and that's true enough as long as the gun is fully within spec. The truth is that dead-nuts feed reliability is in the angles. Feed ramp... Barrel ramp... magazine and follower... and that breechface.
If those angles are correct, you probably won't have a feed-related stoppage over the course of tens of thousands of rounds.
Just some background stuff:
There a 60 minutes in an angle and 60 degrees in a minute.
I minute of angle equals 1" at 100 meters.
1 degree over 1 inch equals .017".
Would .0085" be important on a breechface?
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Would .0085" be important on a breechface?
Apparently so. Otherwise... why would it be dimensioned without any allowable tolerance? The smaller the tolerance, the more critical the dimension.
I was not proposing that .0085" was insignificant. Just attempting to put thins into perspective.
Just reverted back to my machinist/toolmaker background pertaining to dimensional tolerances. The angle is specified at 89 degrees/8 minutes, with no tolerance given. An impossibility, since there's no such thing as a perfect dimension... so... drawing on what I know about tolerances... the angle/dimension must be pretty critical, since the machinist looking at the print is put on notice that he/she/it must take all necessary steps to adhere to it.
That's what put me onto that angle in the first place. i.e. "WHY... in the blue bloody' name of Sir John Moses is it so critical"? (I was a little indignant. The very idea of handing a machinist a drawing that had a dimension with zero tolerance was almost an affront.) It started about 15 years ago, and when I finally got it sorted out, I began to check for it in every pistol that came to me for feed or "eating" extractor issues. The ones that were 90 degrees turned out to be Excedrin Headaches, almost without exception, as did the ones that checked at more than 89 degrees 15 minutes... for different reasons. Those were a little easier to attend to with a good polishing of the breechface... but the ones at 90 degrees... while they responded well to my efforts... never really got to the point that I'd choose that particular pistol if I was faced with having to grab one and run.
The help that the breechface angle might give to controlled feed would become less speculative if some evidence was presented... other than an untoleranced dimension.
I'm not an expert on blueprinting practice, but logically it seems like the more critical the dimension, the more likely to have a tolerance. There is always some error, and you'll never know if you're close enough to a critical dimension, unless there's a tolerance.
Surely no manufacturer in the world would accept "as close as you can get it" on a blueprint, as a tolerance for a critical dimension. And in this case, they may have been able to get it to 1', and I don't think anyone is claiming that 1' would make a difference.
The previous ideas that have been presented about controlled round feed seem likely true: that compression forces on the round are helpful in maintaining control, when the round is in contact with the breech face in the rear, and the frame/barrel ramp in the front.
But to go from this, to the conclusion that the 52' angle is important, is the speculative part. The rough and ready force analysis that we gunsmiths use are very illuminating for the larger effects, but chancy for very small ones like this - unless there is a body of experience to back them.
Folks here have a vast amount of valuable experience, which is a gold mine for us all - but not, I think, with different 1911 breech angles and their effects.
First of all, this angle of which you speak, which end of the breach face has more depth, top or bottom? I'm picturing the angle starting off acute then increasing as it moves down the breach face. Is that correct?
Secondly, how do measure to check a slide for the properly machined angle, 89 deg. 8'? Machinist square? Depth gauge?
Thirdly, does anyone have any idea which companies actually try to machine a slide to that spec? It appears that Colt is hit or miss. What about Kimber, Caspian, STI, etc?
And lastly, is there any accurate method of machining an improperly angled breach face, or would it be easier to just buy a new slide?
GOOD questions, I was wondering also. (Looking at the slide from the side, the angle tapers toward the bottom rear - acute at the top).
Drummer... I use a die maker's square. The angle is as gbw described, raked rearward at the bottom. How many adhere to the correct specs these days?
It tends to be hit and miss. Most do, although sometimes the angle isn't spot on pring specifications. It doesn't seem to hurt anything unless it's either dead vertical or too far past the limit by about a quarter degree... or 15 minutes.
In an earlier haste-induced error I placed that at 89 degrees 20 minutes, when it should have been 88 degrees/50 minutes. I'll go try to find and correct.
Went back to page three and couldn't edit to correct. Stated 89/15 and it should be 88/50. Need to slow down a bit, I guess... but if I do, I can't pack 30 hours into a 24-hour day.
So 88 deg. 50 min. is the correct angle for the breach face?
No. 89 degrees/8 minutes is the correct angle. When it gets too close to... or too far away from 90 degrees is when the problems start.
I'm having trouble finding a diemaker's square that reads to minute of arc. It looks like the most accurate measurement tool available (without too much expense) is a vernier protractor, which will read to 5 minutes. Do you have any further suggestions on a tool to accurately measure breach face angles?
Drummer... The diemaker's square that I've been using for years is an antique passed on to me by my father, and it reads to +/- 10 minutes. It's a Brown and Sharpe, and I don't know if they make it any more... but you might try'em. (I assume that they're still operational.)
The alternative is to use a coarser square and check it by the protractor.
On a final note... No need to fret over it overmuch if the breechface isn't dead on the correct angle. Even at 90 degrees, the gun can be made to run well, but it often requires one particular brand of magazine and sometimes a lot of fine-tuning to make it happen... and sometimes not as much.
The post was mainly to point out a feature of the design that many don't know about or overlook whenever they have to figure a way to rehabilitate a delinquent, non-cooperative pistol. I've faced off with several of these, and aboput as often as not... that angle isn't correct, and I have to take steps to compensate for it... and the thing that works most consistently is found to be the use of USGI hardball magazines, or something similar that provides a late, gradual release that maintains control of the rounds. Extractor modification also works pretty well... and sometimes it takes a combination of several "tweaks" to bring it into line.
So... It can be done. It just takes a little more patience and compromise than a slide that's correctly in-spec.
This is interesting. If I understand this, the angle looks like:
barrel side....\ <--- slash is breech face.
How hard (eg expensive) would it be to machine a gage in an L shape with the opposite angle of 52 minutes off vertical? If the gage mates with no gap, its perfect. A small gap is within Tuner's observed spec. If the gap is too large, the angle was cut too far.
An engraved line in the gage should be the width of the maximum acceptable gap, so both can be eyeballed (with a magnifying glass if necessary).
This post is titled part II, but so fare I have come across two threads dealing with the angled breechface issue:
Learnin' http://forum.m1911.org/showthread.php?t=21924
and
Controlled Feed Study http://forum.m1911.org/showthread.php?t=23342
I'm still looking for the order in which one should examine/measure things when feeding doesn't work properly. Can you make a list in order from most to least likely?
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How hard (eg expensive) would it be to machine a gage in an L shape with
the opposite angle of 52 minutes off vertical?
The problem isn't in machining the correct angle so much as it is holding such a close... read that as zero... tolerance in the angle. When you machine steel, you relieve stress risers, and create others. That causes it to move. It flexes, bends, warps, returns to shape.. .and then moves again. Precision gauges have to be precision ground to size and shape... and then they sometimes have to be lapped to the finished dimensions. Very labor-intensive operations. This is the toolmaker's domain.
The angle is a part of the whole controlled feed sequence, but because it's part of a system that's filled with redundancies that back one another up... it can be a little off and not adversely affect the overall function... at least not to a level that will cause the gun to be condemned as a "Hopeless Jam-o-Matic."
Most often, the indication of a 90-degree breechface is the occasional feed stoppage that has a round that moves all the way up and past the extractor, with the butt-end sitting above the breechface centerline and the bullet nose angled down into the chamber. This glitch may occur frequently, but still chamber 99% of the time, or even more... depending heavily on whether the rim moves completely up and out of the extractor hook.
You can control this tendency somewhat with a little added extractor tension, along with a light modification to the starboard side center pad that allows the extractor to spring open a little easier with the added bend necessary to slow the rise of the rim and keep it from moving past the extractor.
Using a gradual, late release magazine design can also help. The early, abrupt "wadcutter" magazine that releases the round suddenly makes it more likely to get past the extractor hook, while the late/gradual design slows it down and makes it less likely. This is the essence of fine-tuning. Pistols that are fully within-spec in all areas, and fed from magazines that correctly maintain control of the round don't require this sort of thing, very often even WITH the wadcutter magazines or ratty ammo. These are the ones that function with any ammunition without resorting to expensive and time-consuming trips to the skilled smiths. Sadly, such pistols are becoming something of an oddity... maybe one in ten, or even less frequently seen...but there was a time that this wasn't the case. There was a time that you could go out and buy a new Colt, and shoot it for years... decades... and never have a malfunction, with pretty much any reasonable quality ammunition.
I've seen literally dozens of unaltered USGI pistols run happily with the old 200-grain Speer "Flying Ashtray." That was the round that.. once upon a time... gained the rep of being the one that gave shooters the most trouble. It gave rise to the adage: "If it'll feed that thing, it'll feed ANY-thing." And a pistolsmith who could make a 1911 pistol function with that round was considered to be a magician, with accolades coming from far and wide. What they didn't want known was that if the guns were truly right, no magic was necessary. No secret tricks, and no mirror-polishing. Just load the gun and shoot it. Me? I don't mind tellin' it like it is.
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I'm still looking for the order in which one should examine/measure things
when feeding doesn't work properly. Can you make a list in order from most to
least likely?
Well... It's not a very long list, but the first thing to address is the difference between a failure to feed, and a failure to go to/return to battery. The two are sometimes related... but not always... and they're not the same thing. Sometimes a common problem can cause either or both, but most often, it's a different problem for each category.
A failure to feed means that the round doesn't make it to the chamber. If the bullet nose gets into the chamber... even just a tiny bit... the stoppage is a failure to go to battery. Of the two, failures to go to battery is the more common.
Failure to feed... Suspect the magazine first. That a magazine is new... high-quality... comes highly recommended, or whatever... is no guarantee that it's good, and certainly no guarantee that it's in harmony with that particular gun. I've seen many that choked on all the "Gotta have" high-end magazines turn around and run like a Timex watch with ratty gunshow "10-bucks- a-dozen" magazines. The problems with magazines can range from spring tension... follower angle... lip geometry... to magazines being damaged beyond repair.
Failure to go to battery... Can be magazine related, but is most often caused by either excessive extractor tension or hook/tensioning wall relative to the breechface centerline. Next is hook/tensioning wall geometry. The necessity to modify the extractor in order to get the gun to run is an indication that something else is out of spec, and modifying the extractor is a compensation for that. Many smiths will do the standard mods as a matter of course in order to enhance the odds of good function.
It doesn't seem to hurt, and it can help... so it's done, whether or not it's actually needed.
The next place to look is the breechface guide block dimension. I catch this one more often than any other. The distance should be from .484 to about .488 inch, and some guns respond to as much as .490 or beyond... but as a rule, I like to see that width at mid-spec of .486 inch or so, and cut a light bevel on the bottom corner of the blocks.
Then, to facilitate smooth extractor pickup, I like to bevel the bottom of the tensioning wall to follow the block's bevel, creating a ramp that guides the cartridge rim all the way into the extractor. Again... If everything is right, this isn't generally necessary. It doesn't hurt anything, and can be an aid to smooth feeding/RTB when the case rim diameters vary a little.
The next thing to check in either of the above is the ammunition itself. The design is actually very forgiving of ammunition quality and dimensional variations... but there is a limit, especially if the gun isn't well within spec.
Failure to extract and/or eject... The extractor is most often the cause. Insufficient tension is the first suspect. Hook length and tensioning wall location and geometry are next. An extractor channel that doesn't correctly locate the extractor can be at the root of many problems, especially if the channel isn't straight... but rather angles the front of the extractor toward or away from the breechface centerline.
Most malfuctions with the 1911 platform... assuming that the gun is close to being within spec... are usually simple in origin, and simple to diagnose and correct.
Magazines... Extractors... Ammunition. See to those areas and don't overspring the slide... and most problems will disappear.
If metal is hard to machine to 52 minutes, then maybe some plastic injection molding or a Rapid Prototyping manufacture would work.
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If metal is hard to machine to 52 minutes, then maybe some plastic
injection molding or a Rapid Prototyping manufacture would work.
Neither will be very cheap or easy. The tooling still has to be made. Gauges are meant to be used thousands of times in a mass-production final assembly operation. Making a precise gauge to use once or even occasionally just isn't ecomically feasible. Among the simplest and least expensive gauges to make are headspace gauges for a straight-walled pistol case...and a good set will run you about 60 bucks. There are cheaper ones available, of course...but they're not meant to be used for years.
Cheaper, faster, and easier for the occasional user to just use a diemaker's square and verify the angle on a protractor or scale divided into minutes of the angle. If you can find a small tool and die shop, one of the machinists would probably check your breechface por nada. Check first to be sure that the management is gun-friendly, and take the bare slide in the house.
What's fascinating to me is to speculate on how did Browning discover the critical angle, and how did he learn that it must be exact, if possible?
Is there any documentation that gives a clue?
It sounds like he was trying to avoid a hydraulic fitting style connection (90 degrees), or a misfit (88 degrees).
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Is there any documentation that gives a clue?
Yep. The blueprints...
As to how he figured it out, I don't have a clue... but I'm pretty sure that he didn't just think: "Yeah... 89/8 looks about right." There are few features in the 1911 that are so critical as to call for such small tolerances as the angles on the breechface, the feed ramp, the magazine feed lips, and the barrel ramp... which is actually the least critical of the four. Studying the prints will reveal others. I feel pretty safe in saying that those angles and their respective tolerances were the result of a lot of throught... planning... trigonometric and geometric functions and theorums... and plain old trial and error. The 1911 pistol is a study in simple complexity.
Incidentally... Browning didn't have an engineering degree, and is reported to have been quite proud of the fact. He had no CAD/CAM or calculators or any of the modern aids. He sharpened his pencils and worked it out, and likely burned a lot of the midnight oil in the process. Amazing man...
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...Browning didn't have an engineering degree, and is reported to have been
quite proud of the fact. He had no CAD/CAM or calculators or any of the modern
aids. He sharpened his pencils and worked it out, and likely burned a lot of
the midnight oil in the process. Amazing man...
Being an engineer, that's the thing I admire most about him. No one, formally trained or not, has used those modern tools to generate half of the quality designs that JBM produced. Gaston Glock, Stoner, the guy who completed the BHP, none of them bested their own best.
By the way, I reviewed the patent, and unless I missed something, it doesn't mention the breech face angle, nor does it refer to a previous patent on that topic. If it was only specified on the detailed drawings, then it could have been considered a trade secret.
If we made a large scale drawing of the breech face, top of the magazine, rear of the barrel, feed ramp, etc., it might be possible to deduce how he figured out the critical nature of that angle.
My curiosity may never be satisfied...
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It's amazing that anything was designed, built, tested and produced without
the use of computers and computing devices.
All of the best stuff from the century of science (1850-1950) was done without computers. Since we developed computers, significant invention has slowed markedly. Now we make new applications of old inventions. The exception would be in materials.
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If we made a large scale drawing of the breech face, top of the magazine,
rear of the barrel, feed ramp, etc., it might be possible to deduce how he
figured out the critical nature of that angle
Some people have a knack... a "Third Eye" for lack of a better term... that lets them see things in motion before they actually build it and PUT it in motion. Using master pistolsmith Ned Christiansen's practice of mentally shrinking himself down to a millimeter tall, and seeing it work in slow- motion...we can often approach an understanding of the "Zen" of designing working machinery. I've always had a knack for studying a design and figuring out what the designer's intent was... asking myself: "Now, why did he do that?" or "Why did he do it this way?"
I've been trying for over 40 years to crack Browning's code and get inside his head, and a few things are still jumping off the page at me... always there, but hidden to my eyes... until suddenly becoming clear. I'd been looking straight at it all the while without actually seeing it, and I find myself asking: "Now why didn't I see that before?"
Can someone please link to the original angled breech face thread? I have searched but can't find it.
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Can someone please link to the original angled breech face thread? I have
searched but can't find it.
Here ya go, kel.
http://forum.m1911.org/showthread.php?t=21924
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The next place to look is the breechface guide block dimension. I catch
this one more often than any other. The distance should be from .484 to about
.488 inch, and some guns respond to as much as .490 or beyond...but as a rule,
I like to see that width at mid-spec of .486 inch or so, and cut a light bevel
on the bottom corner of the blocks. Then, to facilitate smooth extractor
pickup, I like to bevel the bottom of the tensioning wall to follow the
block's bevel, creating a ramp that guides the cartridge rim all the way into
the extractor.
Can you explain this a bit further, i'm having trouble following your terminology. The breechface guide blocks are the bottom corners of the sides of the breechface, correct? When you cut a bevel on those corners, do you cut it on the parts perpindicular to the breechface, parallel to the breachface, both, or just the corner in general?
Also, what area is the tensioning wall and where do you bevel on it? I think I know the general area you are talking about, I just don't see where a ramp is created.
Drummer... I bevel the bottom corners of the guide blocks to crreate a sort of "funnel" for the case rim. The bevel on the bottom of the extractor tensioning wall does much the same thing, except the bevel helps the case rim to cam the extractor to the right.
Visualize the rim approaching the extractor from underneath. Better for the rim to bear gradually against a ramp than to hit a square corner and force the extractor open in that way. Just makes for a smoother transition into the extractor.
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Cheaper, faster, and easier for the occasional user to just use a
diemaker's square and verify the angle on a protractor or scale divided into
minutes of the angle.
I'm unable to visualize using such large tools in that small internal space.
And which surface serves as the horizontal x axis from which the breechface y axis angle is measured -- the top of the slide, the slide rails, the internal flat surface?
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And which surface serves as the horizontal x axis from which the breechface
y axis angle is measured -- the top of the slide, the slide rails, the
internal flat surface?
The third one... aka Disconnector Rail... and there are some very small diemaker's squares available.
Well... With the angle known... and one side of a right triangle known... a feller could employ triggernometry and figger it out purty easy... if he was so inclined.
No, that's only two things. You need three things - either two angles and a side, or vice versa.
Presuming I had a small enough 90 deg square to lay it on the disconnector rail and stick it up thru the breech, I still don't see how I arrange the protractor to read the angle.
Knowing how they cut a solid block into the shape of the breech would help.
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You need three things- either two angles and a side, or vice versa.
No. You can do it with one angle and one side... I haven't done it in about 17 years, but it can be done. If you've got one side, (B) and an angle (52 minutes) you can imply a side (the hypoteneuse) and go from there to figure for side A.
Making the gauge block would be a snap. All it has to do is lay flat on the disconnector rail, and slide up to the breechface.
This might be simpler?
1 degree is VERY close to .017" over an inch.
52 minutes is ..87 of a degree.
So... 52 minutes is .015" over an inch.
A breechface is about .8" from top to bottom.
So... 012" gap is about right.
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So... 012" gap is about right.
I'd say that'll be about right to within a .0005 tolerance. The only problem would be in tryin' to use a feeler gauge between a dead square gauge and the angled breechface.
Even a pin gauge would give a false read. Close... but still not quite on the mark.
What are the tolerances here - like -0 +? I know it's tight from JMB. Using Go-Nogo feelers placed a few thousands up the face, and dropping the square at them should work. Drag/no drag.
When I was young (I know), 1/2 a thou was a theoretical item.
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What are the tolerances here - like -0 +? I know it's tight from JMB. Using
Go-Nogo feelers placed a few thousands up the face, and dropping the square at
them should work.
Won't work. The gauges have square edges. Loosey at the bottom... GO... Tighty at the top... NO GO... with the same feeler gauge. The specified tolerace on the angle itself is +/- zero.
quote:
If you've got one side, (B) and an angle (52 minutes) you can imply a side
(the hypoteneuse) and go from there to figure for side A.
Cheat -- you are also presuming a 90 degree angle, so that's 3 things.
Anyway, how do you measure that tiny side length to the required accuracy? Magnifying microscope with etched reticle?
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Anyway, how do you measure that tiny side length to the required
accuracy?
That typically wasn't measured, but gauged and accepted/rejected based on the gauge fit. When the standardization was put into efect, the pistols were assembled via the "Gauge/Select-Fit" method with each assembler or sub- assembler on the line equipped with a set of GO and NO GO gauges. If any part, assembly, or sub-assembly failed the NO GO test, the part was usually rejected as being out-of-spec.
I have been following this thread for a while now and have been pondering ways to check this angle without special tools. Using a small right angle machine square, flat feeler guage. and a round diameter wire guage.
Invert the slide so disconnector surface is up. Lets use the calcuations that Lubaloy used in his previous post for a example. Say the gap is .012 at the (vee) of the square. Add half the diameter (.006) flat shim stock or feeler gage between the disconector surface of the slide and the square to shim up the notch of the square . This centers the round gage wire on the O.D. and the square. As the square touches the top of the breachface and the edge of the shimmed square, the .012 round wire gage should just fit through the opening of the notch on the square edges and the corner of the lower breach face on three sides. Too loose and angle is larger, to tight and the angle is smaller. Just a thought.
NightVision... That could work, but ya gotta be careful to get the pin on the corner... except the bottom of the breechface/disconnect rail isn't square.
It's beveled... and the size of the bevel isn't closely specified... so it can vary quite a bit... in toolmakerspeak... from gun to gun. You'd have to determine the bevel, and figure for the correct pin diameter.
If you don't have access to a vernier or electronic protractor to directly measure this angle, the next-best method may be to extend the breech face beyond the disconnector rail as shown in this pix:
This fixture gets the angle being measured out from inside of the inside of the slide for improved visibility and access. Then, Nightvision's method using a good square and feeler or wire gauges can be used. Because trigonometry must be used to calculate the angle, the fixture also lengthens (as it extends) the breech face for reduced measurement uncertainty.
The stock used to extend the breech face should be stiff and straight. If the breech face is convex along its vertical axis or if the disconnector rail is convex, don't even bother trying to measure its angle using this (or any other) method. Both must be flat (or slightly concave) to form an angle which can be measured with any reasonable precision.
And a second bar lying on the disconnector rail would bring the X axis of the triangle up above the slide rails, so you can view directly from the side instead of having to peer downwards. This bar would need two faces and one end to be square.
Before anybody finds that their breechface isn't dead on the correct specs, and gets stressed over it... there are a few things to keep in mind. I only started the thread on the breechface angle to provide information as to why it's like that, and what purpose that it serves... that being a component in controlled feed.
There are a good many pistols that operate just fine with a 90 degee breechface angle. It gets more critical the closer to 89 degrees that it goes, but 90 degrees isn't so much a problem as long as everything else is functioning correctly. The whole controlled-feed system is just that... a system. Everything in the system works AS a system to insure controlled feed, and the angle on the breechface is simply a part of a system designed by Browning in his typical redundant style. That is... every part of the system provides backup to the other, in case one should fail to perform as intended.
A dead vertical breechface functions well as long as the magazine release is correctly timed. Here, we see parallel-lipped "wadcutter" magazines that cause intermittent malfunctions that don't occur with tapered, late release magazines. Conversely, a breechface angle that is too far removed from spec in the other direction may produce maddening faulires to go to battery with tapered/late magazines... and run perfectly with wadcutter-style mags. On the rare occasions that the gun is so badly out of spec in so many areas that it won't run with either... the only recourse is often to start tweakin' the gun itself.
The greatest percentage of feed-related malfunctions are cureable with a different magazine... and it often requires a different type of magazine. Many are addressed with a simple extractor tune-up. The few that don't respond to these tweaks are the ones that require a pro who has the equipment and the know-how to make the guns function.
The good news is that few are that bad, and all it takes is to hit the right combination of magazine and extractor adjustment to make'em run like a Timex watch. The trick lies in being able to recognize that the gun doesn't need more than simple tweaks, and in having the patience to figure it out BEFORE modifications to the gun are made. Far too many guns are compromised or damaged beyond reasonable repair because at the first sign of a failure to feed or go to battery, the tuner/tinkerer buys into the errornet advice to grab a Dremel and start polishing everything.
Very few require mirror polishing unless they have obvious rough, deep machine marks... and even fewer require it to the extent that I see many polished. The breechface is another area that is too often over-polished. All it needs to be is smooth. Same goes for the feed ramp... and if the gun is correctly within spec, the barrel ramp needs no more than light polishing at the top corner... if that. The barrel ramp is NOT a contact point, nor is it a bullet guide. The barrel ramp is a clearance cut that the bullet nose shouldn't contact at all, except at the top corner... and ON the top corner at that.
Many custom smiths will do beautiful polishing on the feed and barrel ramps... not so much because it's necessary... but because it's expected. If you paid 2500 dollars for a full custom pistol, you'd be a little miffed if you saw a toolmark in the ramp areas just as surely as you'd be concerned if there were blemishes in the bluing. The average tinkerer that grabs a Dremel and starts heatin' up the steel... or makin' the breechface look like a mirror may not be helping anything, and could very possibly be compromising the very reliability that he hopes to enhance.
In the beginning, barrel ramps were narrow, because hardball was the only game in town. With its narrow profile and smoothly shaped ogive, it would correctly glide over the top. When the target shooters began to use SWC ammo, with its sharp, full-caliber shoulder/driving band, the "throats" were widened... not to guide the bullet into the chamber... but to allow the shoulder to miss the ramp on its way TO the chamber, and press downward on the barrel in order to prevent its moving up into the slide too early and producing the classic 3-Point Jam.
Most functional issues with a decent 1911 pistol are simple and easy to address without permanently altering the gun... and 90% of these are within the abilities of the average Joe, with just a little instruction and understanding. In nearly 43 years, I've seen only a handful of 1911 pistols that needed more than light smoothing of ramp and breechface surfaces unless they were damaged beyond repair... and those were pretty rough... and I've long maintained that if mirror polishing solves your problem, you've still got a problem... and it will show up again sooner or later.