Oversized chamber in M1 Garand?

[RABAZ]

Shot my non-GI M1 Garand yesterday at 600Y. Good news/bad news: Good is that it shoots well. Bad is that it sheared off part of the case rim on 3 of 20 rounds (see photos). In those 3 rounds, the cases were stuck - had to clear w a cleaning rod. The others ejected fine. I'm shooting .308, at about 2450fps. 40.2gr of N-135, w 168gr ELDM bullets, so not a hot load. Mic'd The cases when got home and surprised to discover that fired case heads measured .478-.480, vs. unfired at .466-.467.

Fired cases (same load) from a different rifle - my AR10 - also in .308 showed only a couple thou in casehead growth.

I'm concerned about shooting this Garand, and thought maybe should just shoot steel cases since they probably won't expand as much?

Appreciate your thoughts on what to do/how to fix!

 

[RABAZ]

Forgot - "NT" brass, in case anyone asks

 

[Blacktailer]

Hey neighbor, are you sure that load isn't too hot??? Shearing off the rim and case head expansion sure looks suspicious.

 

[RABAZ]

Hey neighbor, are you sure that load isn't too hot??? Shearing off the rim and case head expansion sure looks suspicious.

I don't think so - my Hornady Manual says that load should yield about 2450 FPS - and no issues in my AR10 - same load. Actually pretty mild. It's curious...... appreciate your thoughts.

 

[Blacktailer]

You need to chrono that load. Also it appears the pressure is way over when you reach the gas port.
I see N135 is close to 4895 but something is wrong.

 

[RABAZ]

I will chrono the load. But a question - if it was the load, instead of the rifle, why a problem in the Garand, but not in the AR10 with same load?

 

[mtbullet1]

I will chrono the load. But a question - if it was the load, instead of the rifle, why a problem in the Garand, but not in the AR10 with same load?

garand chamber and "function" way diff. than ar10, garands usually do not like full length sizing like conventional weapons

 

[Blacktailer]

garand chamber and "function" way diff. than ar10, garands usually do not like full length sizing like conventional weapons

Yes the gas handling/action function is different.

 

[Harry Knutz]

The most likely cause of this problem is a pitted chamber, When the round is fired it immediately forces the brass against the chamber walls. If there is pitting, It impresses into it, In many cases the case will not extract, It sounds like in your case, It is still extracting but it is stuck for a millisecond, Just long enough for the rim to be damaged, Inspect your chamber, If it's not too bad, You can polish it up. Yugo SKS's are notorious for this problem because none of their bores/chambers were chrome lined.

 

[Harry Knutz]

After looking at pics of your brass you can see the tiny imprints of the pits. The primers are not flattened, But you are getting flow into the firing pin hole, Which is real close to a pierced primer. The firing pin hole may be eroded. I have a rifle that does that too, It keeps shooting without any problems. SO I don't think the loads are too hot, However use a data book that has "Service Rifle Loads" As you can damage them if using the wrong powders.

 

[Harry Knutz]

Polish your chamber and the problem will go away.

 

[orcldba]

The NT brass is mil-spec so the cases will probably have less capacity than commercial brass, just like LC brass.
NT is for Nammo Tactical. Notdic Ammunition is the parent company that owns Lapua They purchased Talley Defense Systems in Mesa, AZ, and have a small caliber loading operation to serve US government contracts. The NT headstamp differentiates the ammunition that is loaded in the Mesa AZ facility from that which is loaded in Finland.

 

[RABAZ]

Polish your chamber and the problem will go away.

Thanks for info. Much appreciate it!

 

[RABAZ]

The NT brass is mil-spec so the cases will probably have less capacity than commercial brass, just like LC brass.
NT is for Nammo Tactical. Notdic Ammunition is the parent company that owns Lapua They purchased Talley Defense Systems in Mesa, AZ, and have a small caliber loading operation to serve US government contracts. The NT headstamp differentiates the ammunition that is loaded in the Mesa AZ facility from that which is loaded in Finland.

Got it. Thanks!