light primer striking problem

[donki1967]

Hi,

My M1 Carbine has a striking problem, but only when the barrel is pointed down...
(Case length is 1.280" and the bolt safety check is ok).

I found some ideas by consulting the carbine forum archives , but nothing conclusive for the moment.
Any help would be appreciated.
Regards

Information

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[floydthecat]

Hi,

My M1 Carbine has a striking problem, but only when the barrel is pointed down...
(Case length is 1.280" and the bolt safety check is ok).

I found some ideas by consulting the carbine forum archives , but nothing conclusive for the moment.
Any help would be appreciated.
Regards

1.280 is the minimum case length. This by default increases head space. I would find some ammo with case lengths closer to 1.287 or so, which is what most commercial ammo measures. In other words….longer cases move the primer closer to the firing pin. If the action is a little lose, short brass aggravates the problem. Minimum trim length is 1.280, but that assumes the action meets head space specs.

[donki1967]

I also lean for a headspace problem, especially since this rifle is a mix master based on RMC, Winchester and IBM parts, but this M1 is very accurate despite everything.
The problem is my available brass is short in length, S&B trimmed to 1.280".

[floydthecat]

I also lean for a headspace problem, especially since this rifle is a mix master based on RMC, Winchester and IBM parts, but this M1 is very accurate despite everything.
The problem is my available brass is short in length, S&B trimmed to 1.280".

There is a fairly easy way to check head space using a case of known length, strips of scotch tape and an accurate measuring tool. If it is much longer than 1.300, it very well might not fire case lengths as short as 1.280. I have known some people to install a longer firing pin and keep shooting.

I’d still be looking for some ammo with longer brass, I just don’t like shooting stuff that short. Of course, you may have some other issue, but you have to ascertain the condition of the action to start ruling-out possible problems. Usually, the extractor will hold the case close enough to the bolt face to fire, but the only explanation for the failure to fire when the muzzle is pointed down, seems to be the case falling deeper into the chamber away from the bolt-face.

Have you checked firing pin protrusion?

[donki1967]

The firing pin protrusion seems to be true, but on the 3 fired cases I can see a primer push back, measured at 0.014 from the case base.

[browningautorifle]

on the 3 fired cases I can see a primer push back

If you're just firing live primed cases, that will happen. There's no chamber pressure to flatten them out. Try a factory new case and prime them to test. You must have a couple factory new cartridges around?

[floydthecat]

If you're just firing live primed cases, that will happen. There's no chamber pressure to flatten them out. Try a factory new case and prime them to test. You must have a couple factory new cartridges around?

Agreed. If primers back-out on fired live rounds, that might be another indication of long head space.

[donki1967]

Jim
The rounds that I fired were live, loaded with 12.2 grains of VITHAVUORI N110 powder.
Nothing wrong with this load, very good cycling.

[donki1967]

Some pics from the fired case

[floydthecat]

I think we need to get back to evaluating head space. Backed out primers on fired rounds really can signal long head space as well as the light-strikes on short brass.

I agree your load is probably ok. 12.1 is the published start for N110.

I will be happy to pm you about how to make that measurement.