If you screw around with 1911s enough, you hear people talk about sprung barrels, especially the bullseye crowd. I know what it is, I'm just curious how gunsmiths measure it. I have an idea, but I cant see any smiths doing this.
So, the question is: How is barrel spring measured?
I have always took the term "sprung" (on semi-autos) to mean simply "screwed up". Poor fit between any of the major contact surfaces of the barrel (not just limited to the lower lugs being fit wrong) that causes inaccuracy and/or malfunction. If this is wrong, please correct me.
Barrel springing is a condition of a too tight bushing and is evident by vertical stringing. It can be determined by assembling the slide with barrel and bushing and with slide upside down on the bench push the barrel into the slide and note if it springs back at all. It should not, the barrel should be free to go as high in the slide as possible and not spring back. The problem occurs as it is the desire that the barrel muzzle make zero movement contact at the bushing when in battery so it can be left too tight. This is a correctable condition by further cutting the bushing clearance just to the point that the barrel no longer springs.
I take it to mean a binding at the barrel/bushing fit that prevents the barrel from properly locking up; the bushing limits the ability of the barrel to properly rotate up and into battery, to the extent that the barrel must bend slightly to allow full lockup. You can feel it for yourself by installing the barrel and bushing in the slide, and then pushing the barrel into hard contact with the slide; the barrel will spring back out of contact when pressure is released. I don't know if you can measure it, other than to determine that there is, or isn't, springing present.
Take the slide in your hand with just the bushing and barrel in it. Push the barrel all the way up into lockup, and while holding it there with your thumb (all the way up into the slide), turn it over so that the lower lugs are pointing up. With the barrel and slide so oriented and while watching the hood, slowly release the thumb pressure. The hood should not move. It if moves up (as the gun is now oriented), the bushing is applying pressure (downward pressure with the gun in normal orientation) on the barrel. That's what is referred to as "springing" and is not whatcha want it to do.
P.S. - Dangit, I must be gettin' even older and slower - log always beats me, but now everyone else startin' to pass me too.
Sheesh! I knew bushings could be too loose, but too tight!?!?!? Boy, you 'smiths don't charge enough considering how easy everything is to screw up.
Thanks for the specifics... The 1st time I heard "spung barrel" used was in regards to one of the lower lugs being cut wrong and not riding the link. Other time it was a bushing/barrel fitting problem, so I just took it to be a general term for fubar barrel fit.
Guys, thanks for the responses! Yeah, that's generally how I have come to understand barrel "spring", but how do you quantify it? Over on another forum (focusing on customized 1911s), a very good gunsmith mentioned that a particular 1911 he worked on by a semicustom shop had about 0.015" of spring. I PM'ed him with this question and got no answer (a LONG time ago...I got busy and forgot about it until today).
So in the interest of enlightenment, I am pursuing the question here. For the only way to know if that is indeed the case, I would think you would need to use a test indicator and indicate on the underside of the barrel along the length.
Also, some question in my mind still exists as to whether this is a real phemomena or not... That barrel isnt much of a lever arm, the caming forces arent much, and the barrel isnt what I would call "flexible" in this sense.
Maybe you could take a measurement somewhere, of the barrel and it's position relative to some part of the ejection port, either at the breechface or the first lug, and compare the measurements with the barrel compressed into the lugs and with the barrel "at rest" with only gravity acting on it?
I can assure you it's for real... The barrel is quite a bit more flexible than one would imagine. Chuck one up in the lathe with a 10ths indicator, and you'll be amazed how slight the force is, which will cause deflection. There is more than one cause for a sprung barrel.. I prefer to use the term, "under tension". The force can occurr in more than one direction. Getting all related parts concentric with one another is essential. Bushings, barrels, bores, and slides are almost never concentric. EGW's bushings are the closest to true concentric I have ever found. Little or no work to true them up.
For the average shooter a small amount of "(tension)", is not a big deal, as long as function is not impaired, but for the extreme accuracy shooters, it is a major issue.
RickB is correct the spring amount could easily be taken from the front of the ejection port, the difference of between zero and where it springs back to. Not that useful of a dimension as figuring then how much to remove from the bushing would be more trouble than fitting to begin with.
You shouldn't use a lathe to do that. You are probably seeing more movement due to the spindle bearings than deflection of the barrel. Even our rebuilt by Monarch 10EE has 0.00003 at the spindle with the class 6 bearings.
I'm going to do some calc's to see what force should be necessary for a 0.001" deflection on a 5" std. barrel. If anyone is interested, I'll post what I come up with. I think it's not going to be trivial.
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You shouldn't use a lathe to do that.
Really?
Monarch 10EE has 0.00003 at the spindle with the class 6 bearings.
That's quite good... you should have no trouble fitting your barrels to zero deflection.
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I'm going to do some calc's to see what force should be necessary for a
0.001" deflection on a 5" std. barrel. If anyone is interested, I'll post what
I come up with. I think it's not going to be trivial.
Cheers!
Calculate away. I think you'll find the amount of force needed to be less than you seem to believe.
I gotta admit I slapped my forehead when I read the OP's comment. So if his lathe has "that much " movement simple math, would deduct it from the big number pressure on the barrel would yield... Okay just went out to the shop and clamped a 5" 45ACP barrel in the vice and set an indicator on the muzzle and found that it was pretty easy to get .020" of flex. And yes the indicator returned to zero upon my arthritic thumbs release. Now deduct the run out from .020" and gee it doesn't change it very much. Thanks that was easy. Calc. away.
Applying that .020" flex to sight adjustment would indicate that is a 2.5" dispersion at 25 yards. Takes a 2" group shooter to 4.5" or more.
In reality it would be more since the divergence begins between the apex of the front and rear sights.
Assuming a tube length of 3" (5" and subtract the length of the chamber and barrel used up in the bushing - had to guess here, no barrels on hand), an outer diameter of 0.581 and inner diameter of 0.452, a modulus of 30,000ksi, one gets:
0.020" deflection takes 230lbs of force
0.010" deflection takes 120lbs of force
0.005" deflection takes 60lbs of force
0.001" deflection takes 14lbs of force
I made the assumption this is a simple cylinder, with the load focused at the end. This also assumes a linear deflection. In reality, the barrel is loaded somewhat more complexly. This is for non heat treated 416. Young's and Possion's really dont change much with heat treatment (some might argure that point ), so...
Ok. I will conceed barrel spring is a real phemonena. I expected less deflection actually. Good call Bob! Now the question is, how much force can the lower lugs exert on the barrel??? This will require a more elaborate solution I think.
Interesting as I was able to get .020" of actual deflection from an actual GM barrel and didn't brace myself and weigh 175#, just a solid push is all it takes to do that. Some times calculations do not take reality into account. You're welcome.
Starts out as an honest inquisitive question, gets honest collaborating answers, takes issue, which is a reasonable response to understanding. But then declares... and doesn't even have a barrel. It's the internet.
I have no intention on getting into any contest here.
But, let me say this. Yes, I was a little suprised at the amount of deflection the barrel had.
However: Log/rrabullseye - yes. I will continue to question everything and everyone. I was anticipating a deflection of 0.001ish with a reasonable amount of force. Thus, if you were to chuck a barrel into a lathe with 0.002 runout, how accurate would you measurment be. Knowing this, how do to ascribe the deflection? Is it the bearing? Is it the barrel? Normally, you would not use a fixture to measure something that may account for a 50%+ error. I didnt need my engineering degrees to realize that.
Log man - a tube is a tube. Steel is still steel. I am curious as to what aspect of reality is not accounted for. Please elaborate.
This is an interesting thread. Should you polish the barrel or fit the bushing at this stage?
Jerry was obviously writing from experience and must have had noticed when zeroing a barrel in his lathe, that it didn't take much pressure to spring a barrel evidenced by the dial indicator used for the purpose of bringing the barrel to zero with the spindle. All presumptions on my part, but pretty easy to have assumed this was the type of experience Jerry was drawing on in his response to the subject.
You discounted it. Suggesting .00003" run out would gave false readings, now saying .002"... but none the less.
You then did calculations that where predicated on believed materials and dimensions. Excellent, reality in the sense that you actually did that, but based on fictitious information that you believed to be correct. No fault. Not actual either.
I clamped a 5" GM barrel by the chamber in a 6" Wilton vise and attached the dial indicator to the vise jaw with a magnetic base. The indicator was adjusted so the stylus was resting against the muzzle opposite from the side that I applied pressure with my thumb. The amount of force was not recorded as I'm not calibrated. However when holding a scale against the wall and pushing against it you will find it difficult to register anymore that 50#. Actual... reality.
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This is an interesting thread. Should you polish the barrel or fit the
bushing at this stage?
If the finish wasn't already a fine finish light polishing might be wise. A bull barrel is fit at the muzzle to fit the slide. So it is the muzzle of the barrel that is reduced in the correct places to affect a tight lock up of the muzzle in the slide.
Inciteful postings don't do anyone any good. This all started with me musing online (making converstation on a dull day) and it quickly spiralled downhill from there.
So in that light I would like to make a few points:
1. Log - The bearing specification I cited was only to illustrate the problems with using a machine to measure something. I believe you have runout confused with a bearing spec. If I lead you down that path, my fault. Most lathes will hover in the 0.001 - 0.002 range unless they are specifically and religously maintained to be more precise. A certain amount of clearence is needed for function. And 0.001 error in a 0.005 measurement is 20%. Things go quickly downhill from there.
2. Log - your vise experiment - I would like to point out a few shortcomings. While I believe you had the right idea (a vise is pretty rigid, right?), there are a few assumptions that lead to error in this. First, you make the assumption you vise is rigid in space. That is only somewhat true. Secondly, and more problematic, is that the vise was designed to hold parts under compression accurately (and even then, they are only so accurate). When you impose the bending force to the barrel, you impose a torsional load to the jaws. The jaws of your vise (or any vise) are not designed to handle that. They likely have a great deal of clearance side to side, and thus would introduce a considerable error in taking a measurement as you describe. In fact, I would be suprised to find that the lathe arrangement suggested earlier wouldnt be more accurate. When you accumulate these errors, 50% or more error isnt difficult to see.
3. Log - As to the validity of the data/relations I used to estimate the deflection. They are all but chiseled in stone now. What do you suspect? I dont think they are "fictional" by any stretch of the imagination.
Perhaps a very low quality lathe would exhibit spindle run out of (.001/.002), but mid range and higher lathes all offer spindle run out in the tenths... and preloaded tapered bearings do operate with out clearance or free play..
quote: I would be suprised to find that the lathe arrangement suggested earlier wouldnt be more accurate.
The lathe I use for the "fixturing" / and very precise measuring, which I mentioned, is approx. 4000 pounds with a chuck that is in the neighborhood of 100 pounds. Quite stable and suitable for the job.
It produces barrels and chambers in the very low tenths... holding 1 or 2 tenths on most guns is very good by any standard. Maybe not 3 / one hundred thousandths like your Monarch, which is only one decimal away from millionths! but still very good. Which brings up a thought. It's pretty difficult to accurately measure .00003 with a standard pressure displacement indicator/tester.
Just a note that the vice in question isn't in question as it is equipped with roller thrust bearings and capable of several tons of pressure. I know this because I equip my vices this way and they will press in a pin that a three ton arbor press can barely do. So 50# pounds isn't going to flex the jaws. And the real point is you admirably used paper and I used the actual element in question. Moreover the results show that barrel springing is not a phenomena but the mechanical result of a too tight fit bushing, and can be measured which was your question and answered by several of us. But that measurement is only valuable in conversation, as zero is the goal and obtained by fitting. Jerry uses a sine plate fixture and dimensions to establish just where zero is and his methods are perhaps hard to understand , but unquestionable in result.
Perhaps the fact that the slide stop pin will apply pressure on the lower lug and the bushing is holding the barrel at the muzzle 4.375" away, and when I actually clamped an actual barrel not a virtual one which was only 3", I clamped it by the chamber end next to the lower lug, so my thumb was applying pressure over 4", not 3". Would change things and account for a difference of results.
LOG - yes, indeed that does. Which is why its always good design practice to have your work reviewd by someone else! For example, that change in lever arm would make 0.020 deflection require a 100lb load. Now we are getting somewhere!
As for the vise. What you have described alludes to the mechanical advantage afforded to you by the Wilton in comparison with an arbor press. This wont affect accuracy or precision however.
We have answered the question of whether or not a barrel flexes quite well. Unfortunately, we still have not answered the question of: how do you measure the spring in a barrel? I may not have been perfectly clear earlier however. I am not so much interested in measuring how much a tube bends under load (that is trivial and academic). I am concerned with measuring spring of a barrel in a 1911 that is assembled. It just occured to me that was the question I was thinking, but not necessarily asking.
I'd like to say that this is the first time I argued over 0.001 of an inch! Unfortunately, I can't...
ETA: for those keeping score, that is roughly 33,000 PSI bending stress on the barrel!
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I am concerned with measuring spring of a barrel in a 1911 that is
assembled.
This is of course done with only the slide, barrel, and intended barrel bushing. Wanting to measure the barrel spring amount when fully assembled is like wanting to measure engine valve lash without removing the valve covers.
When fully assembled a too tight bushing can mimic a tight barrel fit in feel. A tight fitted barrel should feel the same with a known loose bushing versus the fitted one. If it feels tighter, closes with more resistance, then the fitted bushing is too tight. The goal when the gun is in battery is the barrel has zero movement with zero tension.
I have had an excellent off line conversation with BLR. I believe him to be an honorable man and I apologize for my public rudeness. While our testing methods are not on the same page, I believe he is simply in search of knowledge and understanding of how 1911's work and why they work that way.
Small lesson here in barrel fitting and springing from an amateur. Proof springing and torquing robs consistancy and accuracy.
A Kart barrel I fitted developed a nick in the muzzle when I withdrew the cleaning rod too far and was already in forward motion mode. Well the edge of the cleaning rod got the muzzle. Yes, I was using a muzzle guide and just wanted to quick scrub the barrel. Go figure. Anyway...
I couldn't stand my "special" 1911 having a nick in it so I had another Kart in the box and fitted it. It shot well, but once in awhile, it would throw a shot or two out of the group. Not consistantly, but not rarely either. I ruled out the loads when it did it with all known good handloads.
So I settled down to do some real close looking at the wear patterns. Not wanting to remove any unnecessary metal, I examined the wear marks and noticed it was hitting harder on one lower lug and opposite side lateral hood extension surface. I touched the hood surface a few strokes, marked, assembled, cycled and examined the fit. Couple strokes on the lower lug. Did the assembled dry run routine. Seemed right. I went to the range tried the pistol. It worked. The fliers were gone and it even cycled smoother.
Moral: Sound barrel fitting is far more beneficial than a super tight fit which is loaded and torquing as this barrel was.
For the record, I bought the Brownell's muzzle chamfering and deburring tools and used the nicked barrel in another pistol I built. It was my main competition pistol for several years before I sold it. It shot very well with that barrel in the second gun.
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Maybe you could take a measurement somewhere, of the barrel and it's
position relative to some part of the ejection port, either at the breechface
or the first lug, and compare the measurements with the barrel compressed into
the lugs and with the barrel "at rest" with only gravity acting on it?
Or if you want to get complicated, put a known "sprung" barrel in a slide, put the slide upside down into a vice with enough clearance underneath to get a last-word indicator on the top (now the bottom) of the barrel hood, push down on the barrel, zero the indicator, and then release the barrel and see how much movement you get.