Can we discuss the reliability of M-1 Carbines?????

[bonnie]

I cannot cite the source for this information but have used it for many years:

A new USGI 15 round magazine should measure 1.5 inches from bottom of retaining lug to top rear of feed lip using a micrometer. I found this to be a good way to check a good magazine that has gone bad. Usually find the measurement is well under 1.5 inches indicating the magazine retaining lugs are too worn for reliable feeding.

[USGI]

I've heard the 1.5" spec. before too, and consider it a "ballpark" figure. The only mag failure I've had over the past few years was on a "new" condition KSG Type 1 that had the lugs strip almost clear off the very first day of use. The mag dropped down so low that it would not allow rounds to feed.

The last several times I've gone out to shoot any of my carbines, I've been using the same (3) very worn looking mags: an IA, and two KSG's. I shot 6 boxes of reloads through my IBM in July using those three, loading them with strippers, and not paying any attention to which mags were in the gun. I had (2) stoppages (failure to feed) occur and never paid too much attention, other than figuring it was probably caused by the mags. After seeing this thread a few days ago, I measured all three of the suspect mags and found one of the KSG's to measure about 1.460" from the lugs to the feed lips. The other two measured about 1.480." Kuhnhausen's shop manual shows the spec. for this as 1.523" +/- .002". I have a very nice "U" mag that measures 1.490" and I just measured a new 10 rd. commercial mag and a 5 rd hunting mag (with the lug on the side) and they both are about 1.490." I've got several brand new USGI 15 rounders, but have never measured any of them. I used a dial caliper with one jaw across both lugs, and had the other jaw where it just contacted one of the feed lips at the very back of the mag. I'm going to mark the mag that measured 1.460" and see if it's the one giving problems next time I go out to shoot. I agree about the chamber needing to be clean. I've had powder residue or something build up in there, and it caused the appearance of tiny dents all over the cases when fired - it kept on functioning OK, though. - Bob

[imarangemaster]

I have found that most aftermarket magazines use thinner sheet steel for their magazines, making them looser. This is especially true with the 30 rounders. Their lugs wear faster, and sometimes are less pronounced than GI.

[firstflabn]

I appreciate Kuhnhausen's work since I don't have the shop drawings and I refer to it a lot, but it should be remembered that .010" is 2-1/2 thicknesses of a sheet of copy paper. Might be that much growth from thermal expansion after firing a mag or two.

The system is composed of many parts that work together. The effect of a mag that's a few thousandths short could not be evaluated without knowing the relationship to the feed ramp. Would be interesting to see how the drawings detail that complex shape. A mag that's too short could be compensated for by a feed ramp that's cut (or worn) just a hair too much.

The intricacy of the design is so fascinating. Think of all that has to go right for the band spring to grab the barrel band properly. Receiver ring lip, recoil plate cutout, band spring hole, band spring notch, barrel band width, stock length, handguard length. All that for a static system that, other than the buttplate fit, is likely the simplest in the whole weapon.

A tolerance miss doesn't guarantee failure (except you can't have negative clearance), but makes failure from tolerance creep more likely.

[ABPOS]

I know that at least two of the mags I have are USGI. One is an IS and I forget what the other one said. I was just looking at it the other day.

---------- Post added at 02:40 PM ---------- Previous post was at 02:39 PM ----------

I have been shooting and carrying M1 carbines as LEO duty weapons since the early 1980s. I could count the malfunctions in my personally owned and maintained carbines from tens of thousands of rounds on one hand. I SCRUPULOUSLY maintain my weapons, since for 25 years my life depended on them.

1) Make sure recoil spring is close to 10 1/4" long: degraded, short, weak springs can cause malfunctions
2) I have never had a malfunction with a US GI 15 round, and only several through the years with USGI 30s. There are no aftermarket 30s I trust, AT ALL!
3) make sure mag spring is in the right way: /\/\/\/\/\/\/\/\ long side to the rear
4) Make sure it is lubed properly
5) avoid some commercial reloads. BAC makes good ones, as does Georgia Arms. Avoid Aguilla ammo. underpowered, 150 to 200 fps slower than USGI. I use magtech or RP ammo exclusively.
6) a very sloppy trigger housing can cause malfunctions because it holds the magazines aligned with the receiver. I had a firends carbine that did this, DO NOT try to pinch the bottom lugs of the rear of the receiver tighter. They will snap off You can modify the lug on the trigger housing to be tighter.

Can I clarify something in your post here? When you say "long side to the rear" for the mag spring, do you mean the peak should be at the rear?

[emmagee1917]

Yep , carbine is backward from BAR , 1911s , Springfields , etc.
In his drawing , the bullets would be pointing up.
Chris

[ABPOS]

So the highest part of the spring is supposed to be at the rear? I'll have to check my mags. I think they were like that, but yeah, it seems like that would promote nosediving, making it harder to feed.

[imarangemaster]

The carbine mag spring pushes up the cartridge base snug against the rear of the lips of the mag. A guy who had a class III shop had fits with his registered M2s feedong and had me work on them. All 4 magazoines he had had the springs in backwards. Switched them around and they fed fine. One even had the spring from a 15 rounder stretched out for the 30.

[ABPOS]

I'll definitely double check my mags.

[DaveHH]

I've always wondered if slamming the magazine in with the palm is detrimental to the health of these magazines. The system is really fragile when compared to say an AR. Additionally, were the 15rd magazines viewed as expendables thus many millions of spares produced?