In the now-closed thread "Tuner, 1st Test Results..", conflicting dimensions were given for the vertical distance down from the frame/rail top to the feed ramp bottom. In post 19 one poster gave 0.400 to 0.420 inch. In post 21 another poster gave 0.320 to 0.400 inch for this same distance.
Neither of these are correct. The correct dimension is given in the following illustration:
These dimensions were derived from specifications contained in U.S. Army (Rock Island Arsenal) blueprints for the M1911A1 receiver, last updated during the 1970's, available via link in the Technical Issues section of this forum.
Thanks for this informative post... I always enjoy your diagrams, as they make understanding the discussion that much easier! For us *new* guys... being able to see the discussion is the difference between a whole bunch of numbers being quoted and actually understanding how they fit into the puzzle.
Yeh. +/- almost a tenth of an inch kinda tells ya how critical it is...
Thanks for the drawing, Niemi. I've been checking the frames on some of my guns and there is certainly a wide variation in dimensions from frame to frame. That's a bit strange, since the relationships in the frame bridge area are critical and determine whether the gun will feed reliably or not. Either the various frame manufacturers really don't know the correct dimensions, or their machines are so sloppy that they can't produce them consistently. Not a very encouraging picture!
These variations found in as-built frames could also result from tolerance stacking. As 1911 Tuner noted above, the tolerance for these calculated dimensions involving the barrel bed, frame feed ramp and magazine well are indeed rather large.
The major contributing factor to their largeness (?) are the rather large tolerances in the basic dimensions which locate the feed ramp and mag well from the slide stop hole, both of which are -0.01 inch.
A quick scaling showed that just changing both of these dimensions within their tolerance limits will, by itself, see a 0.070 inch vertical shift in the mag well/feed ramp junction!
When all the other tolerances get factored in mathematically they all pile up (stack) - especially the +/- 0.5 degree tolerances on the angles.
Don't think the frame manufacturing picture is quite as bleak as you paint it. Tolerances lead to variations. Large tolerances lead to large variations. As me dear departed Mum was fond of saying, "Variety is the spice of life".
And what's the frame bed to the frame rail top dimension? I mean that's something that can be critical, from what we have seen here.
From an earlier Niemi drawing, .077" +/- .005", I believe.
Hi John: Distance from the frame/rail top vertically down to the frame bed (or barrel bed) works out to 0.077 +/- 0.005 inch. That, of course, is for a new & untinkered-with frame made to U.S. Army (RIA) specs.
Guess I should have included it in Post #1's pic, but edit time is now over. I'll put together a pic with these and all the other derived dimensions for the frame ramp if you or anybody else wants to see them all in one place.
Just give me the word.
BTW, I've been calling that curvy place in front of the frame feed ramp a "barrel bed" for some reason, but lots of folks call it a "frame bed". Which is the preferred term? Cheers
I'd sure like to see them, if we're voting.
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Hi John: Distance from the frame/rail top vertically down to the frame bed
(or barrel bed) works out to 0.077 +/- 0.005 inch. That, of course, is for a
new & untinkered-with frame made to U.S. Army (RIA) specs.
Guess I should have included it in Post #1's pic, but edit time is now over. I'll put together a pic with these and all the other derived dimensions for the frame ramp if you or anybody else wants to see them all in one place.
Just give me the word.
BTW, I've been calling that curvy place in front of the frame feed ramp a "barrel bed" for some reason, but lots of folks call it a "frame bed". Which is the preferred term? Cheers
Just edit your picture to add that dimension and re-upload it to your pictures hosting server using the same name as the picture in your first post here.
And if you come up with some more drawings, add them here.
As for the terminology, I think I am using both terms interchangeably. I do not know what is the right one!
Couldn't figure out how to get Photobucket to really delete the original drawing put in Post #1, so had to put the updated one here.
Still working on the drawing with all the other dimensions around the bed and ramp.
Niemi, have you come across the correct BARREL feed ramp angle in any of your figgerin's?
Gbw, remember one of Tuner's recent posts that pointed out that the "barrel ramp" is actually a clearance cut? In that sense, the exact angle is not too important as long as the bullet nose hits the top of the barrel ramp only. The actual amount of metal removed is going to depend on how much brass is exposed at the top of the ramp. A figure of .090" exposed brass is suggested as a working maximum by J.K. - that includes the effects of dynamic headspace.
Hi GBW: I had previously posted both of these, but I'm not smart enough to either have kept track of which thread they're in or to use the forum search tool to find them.
So, here they both are - one for each type of USGI barrel ramp. The barrel ramp for the U.S. Gov't National Match barrel might be different from either of these, but I don't have its blueprint - even though I've got one of those barrels.
I've no idea which is of these is the best ramp style. Regards
P.S.: Oops! Didn't mean to start a new thread with this. Had intended on posting it in "Dimensional Conflict".
I do recall. Still, I'm thinkin' that the gov't drawings, as detailed as they are, will either give directly, or imply a spec. angle. And the fact is that with all of the oddball bullet cartridge combinations we shoot, and the wild variations in frames and barrels, the barrel ramp is going to get hit now and then despite our best efforts.
Another question - does the .090" include the rim thickness of the cartridge? It doesn't look to me as if it could - see at the photo's in the 'COAL - Hmmm...' post. Also, I'm pretty sure that Niemi (that guy is priceless), gave a figure for max exposed brass INCLUDING the rim in one of our measuring threads a few weeks back. I'll look it up when I get mor time.
Meantime, if JKs .090 doesn't include the rim, where is the index to begin the measurement?
Many thanks, N. My homework for tonight was going to be to research these - I remembered that you had done them. They are excellent!
Negative, gbw, the .090" figure does not include the rim because that part of the case is not going to give way in an overpressure situation. Your critical area is going to be ahead of the case bevel, so the measurement starts at the junction of the case bevel and case wall.
Thanks Niemi. My first thought is that the actual shape of the barrel ramp isn't important, since the bullet will only be in contact with the top edge.
On the other hand, no barrel ramp contact is the ideal, and I'm not certain if we are dealing with another statistical average situation. If the gun is built right, do all the rounds miss the barrel ramp, or just most of them?
My third observation is that most of the "pre-cut" barrel ramps out there are concave in shape, conforming to neither of your drawings. Intuitively a concave shape would seem to be the least desireable since it would tend to "trap" a bullet tip rather than guide it smoothly upwards.
In my limited experience, I save barrel ramp adjustment, if any is needed, as the last thing to do before smoke testing.
Humpf... now it sounds like too much, at first blush.
Hi Lazarus: Got a feeling you're correct in saying the actual shape's not important. Maybe the reason the straight alternate cut was added (only the radiused cut is shown on the 1940's vintage SA blueprint) is because it might be easier to machine.
Whether all or just most of the bullets miss the barrel ramp is an interesting question, but finding the answer for a well-tuned gun would, I think, be sheer agony. You'd have to mark at least the barrel ramp and check it after each shot was fired until contact was detected or (if no contact was detected) it was shot enough times to say the ramp never gets hit. That doesn't sound like fun shooting to me!
Concave barrel ramps, huh? Maybe the thinking is if the ramp needs to get moved forward during the fitting process, there's less metal to have to whittle away. Or, maybe something to do with the machining process. There's probably somebody out there in 1911-Land that knows for sure, but it's not me.
Look at the frame to barrel gap again. "-.024"" would leave quite a barrel overhang!
Hi David: It sure would! However, that's just the way the tolerances pile up (accumulate) when doing the math. Although all of the parts would, individually, be within tolerance (at their limits), I'm guessing a gun assembled with such parts would fail some sort of QA check during assembly.
Heck, if it would ever chamber a round I bet the bullet would whistle all the way down range from the big nick it got!
Here's the drawing mentioned in Post #8. It has, I think, most of the dimensions needed to troubleshoot a gun with suspected bed/ramp geometry problems.
Some will grumble that the tolereances for the various feed ramp dimensions are much, much too large. However, when making 10 calculations using 6 different toleranced dimensions to arrive at, say, the feed ramp length, these tolerances accumulate, pile up, and stack. And I don't know any way to avoid it. If you know a way, please share it with me.
PICTURE 404
As usual, these specifications are from U.S. Army (RIA) blueprints for the M1911A1 available via link in the Technical Issues section of this forum.
.300 feed ramp from the deck of the frame to the bottom of the ramp is not workable with Hollow points and 8 round mags.
.400 works with about everything. That would make me the .400 to .420 guy
More often than not today we end up lowering barrel beds to allow clearance of match barrels. Probably 2-1 need the beds lowered.
geo, www.egw-guns.com
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.300 feed ramp from the deck of the frame to the bottom of the ramp is
not workable with Hollow points and 8 round mags.
Hang on to yer end mill, George! Check-Mate is about to rewrite the rules on 8-round mags. What would you say to a genuine flush-fit 8-rounder that'll feed hollowpoints into 2 stock Remington Rands and an untweaked 1919 Black Army Colt? I've got four of'em in my hands that do it without fail... and you know how much I hate 8-round magazines...
Whoa! Hold on there a minute, Mr. Tuner! I've been on this site 3 whole months. Just long enough to learn to trust you purdy expicitly... Now! You come along and tell me/us that all your previous bologna was... well... bologna? That is pronounced bolony for those who might not have bought the cow teat stuff. I like it, so I can say it... Anyway... I've been moanin' and groanin' as I progressively have been getting rid of my 8 round mags and started learning to count to 7 (+1). Now you tell me to count to 8 again??? And right after I order all those 7 round mags on the big buy? I think it is time for you to come to Arkansas and buy me (at your expense) a whole Single Sonic Burger. I should demand cheeze, but I am easy.
You had better test, test, test, dude! You have influenced several of us to "do what you say". Actually, if what you say is true, I will be greatly delighted! Get some volunteer guns and more mags and fill us in.
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Whoa! Hold on there a minute, Mr. Tuner! I've been on this site 3 whole
months.
Yep. I know, David... and up until Check-Mate started development on this thing, I had about as much use for (the current crop of) 8-round mags as I had for a longslide 1911 in .32 ACP caliber... but like I said. They rewrote the rule book. I figured that it would only be a matter of time before somebody hit the magic numbers.
The prototypes that are in the development/testing phase have shown a lot of promise. Still a little issue with the springs... specifically longevity under hard use... but that's a simple matter to address. They'll get it.
Disclaimer:
I have no vested interest in Check-Mate Industries. I have received no free products from the company, other than 6 test magazines and 4 upgraded springs. I have in no way been compensated for endorsing their products, nor am I being compensated for aiding them in the research and development of their new magazine design.
It must be those "Hybrid" feed lips... or is there more?
Is the mag body different from their 7-rd mags (Hybrid or Gov't)? In other words, will it be possible to convert any existing 7-rd mags?
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"Hybrid" feed lips... or is there more?
There's more...
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In other words, will it be possible to convert any existing 7-rd mags?
Yes... and if anyone does, I'd like to buy their 7-round followers. I need about 30 of'em.
If the ethereal CM group buy ever actually happens you'll probably get all you need. But it's been so poorly handled and / or communicated I'm beginning to wonder if it will.
Most folks, like me, ordered 7 rounders. I'm perfectly happy with 7, but I'm thinking many will happy to know they can upgrade / convert.
This thread is completely off topic now, but in order to have 8 rds. in a 7 rd. tube, CM has to modify the follower by making it shorter. Wouldn't it be easier, and work better, if they just lengthened the tube to allow for 8 rds and the standard follower, like the Tripp Researh Cobramags?
George, if you don't mind, I have some questions in response to your earlier post.
a) what do hollowpoints have in common with 8-round magazines that calls for lengthening the frame ramp?
b) when you cut the ramp longer, do you keep the 31.5 degree angle, or do you make the ramp steeper so the top edge of the ramp will not move forward?
c) The NM barrels by design have extra material (sometimes in all dimensions) for more fitting options. Wouldn't it be a better idea to remove extra material from the belly of the barrel rather than cut the frame bridge lower? (i.e. the frame is the more expensive part).
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b) when you cut the ramp longer, do you keep the 31.5 degree angle, or do
you make the ramp steeper so the top edge of the ramp will not move
forward?
An excellent question. If you keep the same angle, do you then have to move the barrel ramp toward the muzzle to maintain the frame ramp to barrel ramp gap?
I've also had to lower the frame bridge on every Caspian frame I've used (4), between .010" and .022" depending on the slide / barrel combo.
I'm not George, but it seems like the reason for the 8 rd. magazine being problematic is twofold. First of all, the more rounds you have stacked in a magazine, the more gap there is between them, and therefore less support for the feeding round, allowing it the opportunity to nosedive. Secondly, with more rounds comes more spring pressure causing more drag on the top cartridge, creating more tendency to nosedive. Put them together, and that may be the problem that George was speaking of.
I would think that it's exacerbated by the shorter OAL and flat-nose shape of hollowpoints.
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but it seems like the reason for the 8 rd. magazine being problematic
is...
Well... Kinda close, but there's more to it than that.
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Well... Kinda close, but there's more to it than that.
I guess kinda close is better than totally wrong. So, what's the rest of the story?
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Tunefucious would suggest that you start with "Function of the Dimple" and
"Inertia." Much light will be shed on subject of most troublesome 8 round
magazine.
A few more readings and I'll have 'em committed to memory
Couple what I said above with the fact that most 8 rounders, ok all but Cobramags and the metalform Elites, have shortened, less stable followers, lack dimples, have the straight wadcutter feedlips, and sometimes suffer from underpowered springs, and you're tempting fate.
That said, it would seem like the best way to get a reliable 8 rounder would be to just lengthen the tube enough for one more round, use a slightly longer spring, and then use the standard dimpled follower and "hybrid" feedlips.
Revised Drawing
This drawing replaces the one in Post #23. It contains 2 new dimensions (shown by the broken lines), a minor reduction in ramp length, and a major reduction in the ramp length tolerance.
If your gun has feeding problems and you suspect it has ramp geometry problems, these dimensions (derived from the U.S. Army blueprints available in the Technical Issues section) may prove useful along with that blueprint data.
