What's Causing My Cases To Break In The Chamber

[railroader]

Have experienced several ruptured cases that have torn in half recently, and was wondering if anyone out there has had this problem at any time. Could it be that the bolt is trying to extract the shell before the pressure has subsided? If so, would this be caused by too hot a load, or a problem with the blish lock? Any advice appreciated.

[TheGunny]

Can you post pictures of some of the ruptured cases??????

 

What type of ammo?????????

 

Is it a Kahr????????? http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/blink.gif

[Sgt]

We probably need to know what gun you are shooting. Assuming it's a Kahr, that is not an unusual affliction. When I first got my Kahr it would shoot out of battery. It would do what you described. It appeared to go off without being fully chambered, splitting the side of the casing. I'm not sure if that was happening as it was going in or coming out.

[reconbob]

Are you shooting reloads? If so, resizing work hardens the brass, increasing the possibility of splits which become ruptures under chamber pressure. If you are shooting a hot load you may also be over-working the brass

with the potential for a similar failure. Hot loads increase the velocity of the bolt assy. which is not a good thing.

If its not the brass its because the cartridge case is not properly supported by the wall of the chamber, and under pressure the thin wall of the case is stretched beyond its elastic limit causing split/rupture.

My experience has been that these failures occur mostly when the cartridge is fired when not fully seated, as opposed to occuring during recoil. The pressure time curve of .45 ACP like most pistol cartidges is very steep and

peak pressures dimish very rapidly.

So, why does the gun fire out of battery....

 

- dirt/foreign body in firing pin assy. causing firing pin to stick at times causing early ignition, not

helped by weak or worn out firing pin spring - if round coils are flattened with wear replace. Also

check to make sure hammer is not sticking.

 

- dirt/powder residue (especially unburnt powder) build up in chamber eventually causing cartridge to

stick when being fed into chamber & being ignited just before being fully seated. If your ruptures happen

more as you fire more this could be it.

 

- if additional cases look like they could have ruptured but didn't, you may have developed a chamber

problem, nicked, jugged, etc.

 

There are a couple of other possibilities, but a) ammo, http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/cool.gif dirt/fouling is most likely.

 

Bob

 

 

[JimFromFL]

Are you using factory or reloads??

 

It may sound strange, but take a video camera to the range to capture the problem then you can play it back is slow motion to help determine when/if the round is firing out of chamber.

 

[giantpanda4]

You mention problem with the blish lock. That makes me assume your gun is a 21/28 of some flavor. That also means that it does not have the fixed firing pin, as in a M1A1 bolt, which is the usual cause of out of battery firing. I would then tend to agree with Bob that maybe your bolt assembly is dirty (ever fire corrosive ammo? and then forgot to clean out the bolt - like I did ONCE?). Try cleaning and oiling. and give us the rest of the story, ammo - gun - reloads or not, etc.

 

The video is a great idea as well! Or , if you shoot left handed like me, just keep your right eye open... http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/laugh.gif

[PK.]

The failure described “cases that have torn in half “ implies to me that the front of the casing is still in the chamber and, in the case of a 21/28 model gun, the round subsequently fed simply stops on this broken case. I seem to recall a recent post describing this same scenario.

 

In my experience, this is most often caused by well used brass that originally had an axial crimp applied to the case at the base of the bullet. This creates a line about the case that is more prone to fracture. It's more likely to happen in the SMG because of the generous chamber dimensions as compared to the pistol.

 

If you are loading a lot of such brass, it’s time to retire it.

 

 

 

[railroader]

Thanks to everyone who responded about my problem with the case rurptures. I' shooting a 28 West Hurley with all GI internals. I don't recall having this problem with factory ammo, only when I started using my reloads. My loads are Unique, 6.5 grs FMJ, and 5.8 grs with LRN, both 230 gr bullets. I have noticed the the gun gets dirtier than heck using Unique, and have been thinking about using Winchester. I also noticed the last time I shot, I dumped two 50 round drums of lead round nose without the gun missing a beat. (the lead makes a mess). Then went to my stick mags with FMJ and had the case rupture. The case ripped in half about midway. Maybe it was a combination of the lead along with some powder fouling from the Unique that caused the problem. Thats what I'm hoping for anyway. Will try shooting nothing but factory loads next time, and see what happens. Stay tuned for more of "new guy with a Thompson ".

[21 smoker]

This is a routine accurance for me and it is always a reload with a cannelure about half way down from the mouth...imo it is case fatigue..plain and simple. I carry a Trapdoor 45-70 broken case extractor on every range outing,..5 minute fix..hth.. http://www.machinegunbooks.com/forums/invboard1_1_2/upload/html/emoticons/wink.gif

[JimFromFL]

To the original poster:

What brass is being used? I hear others mentions some brass like PMC or the Federal in the blue box (i think) are not the best brass to use.

 

To others

Just wondering, would this issue with what you described, leave a bulge or any minor disfiguring to where it would NOT fit in the case gauge.

 

[guy sajer]

I only own 1 tsmg . A Savage M1 . The chamber is a little large [dia] compared to other .45's I shoot . I assumed the military chambers were a little loose to allow for dirt and fouling ?? Fired casings stretch further when fired in my Savage . The sizing die will do it's job , but the brass gets a good workout and sooner or later the case will split . Usually after between 5-10 loadings . I consider this normal attrition .

[railroader]

Update on my broken shell problem. To clarify, I'm shooting a full auto,

28 West Hurley. Took it out today and ran one 50 round drum, and two 30 round mags of factory Federal (red box) without the gun missing a beat. Then, ran a drum of 50, 230 gr FMJ reloads using 6.5 grs of Unique. I had two case separtions. Rather clean circular case separation just about midway on the case. I'm not sure how many times these cases have been reloaded, but it can't have been more than 2 or 3 times. I measured the spent brass, and all seem to within factory specs. The problem appears to be my reloads and the Federal brass, but I can't be sure.