MG42 reloading, Brass shrinkage????

[Waffentag]

Well, The MG42 has been running great in 7.62 with reloads. I relaoded some surplus 7.62 NATO cases twice and thought that I would need to trim my brass. However, it was actually shorter than when I started? Now, I have been relaoding for over 30 years and have never seen this? Is it even possible?

[JBaum]

Don't know about the short brass, but 3 firings on one piece of brass is usually the limit for me. After the third shot, there are severe stress lines (dark streaks) down the side of the brass which is where they will split if you shoot them again. I've had some brass that could only take being fired twice. After 3 in an MG42, I put them into the scrap brass bucket.

[Waffentag]

I just measured and resized every case from my last shooting session. My Gage or my eyes must have been off when I checked a few before and thought that they had shrunk? They did not shrink! In fact, about 1/2 are are now over 2.015, (7.62 NATO). Perhaps, by luck, the few that I checked before were a differnt lot?

I must say, of all the reloading tasks, I really hate trimming, I am almost to the point of just buying new brass when it comes time to trim. I even bought a Lee trimmer that fits in my old single stage press and that I can hook my drill on.

So, how important is case lendth when shooting the MG42 in 7.62 NATO using west German Barrels?

[JBaum]

If the front edge of the cartridge hits the front of the chamber and doesn't let the cartridge go the whole way forward at the back (effectively causing excessive headspace), you could have an out of battery explosion.

I haven't had any problems with overall length when limiting the use to 3 shots total. Very few guns can be as hard on brass as the 42, so the usual "once fired" stuff is what I use to reload, and after one more reload, I don't worry about it and put it in the scrap bucket.

[Waffentag]

Thanks John, I understand that if the the OAL cartridge length is too long that or if the case head space, base to shoulder is too long that could cause the round to fire out of battery.

My question is how much free bore does a German MG42 7.62 NATO barrel really have? All the reloading manuals say that max case length is 2.015. I have read that military barrels have a lot of free bore, the free space before where the lands and grooves start. I understand that if the OAL cartridge length is too long, that the bullet hitting the lands and groove causes high pressure and a possible OOB.

So, if the shoulder headspace and OAL are good, what we are really talking about is a slightly longer case neck sticking into that free bore area. So, how much does an MG3 barrel have, 2.015, 2.025. 2.035? Am I trimming cases that spec 2.18 for no reason?

Pat

[JBaum]

The only way to know what you have would be to measure it. What I have is irrelevant and shouldn't be used to judge what's safe for you. Stick longer shells in until they won't let the bolt rollers lock, and then you'll know.

[Waffentag]

Ahhh, That is smart. I was wondering how to measure a chamber free bore space without making a chamber cast, one would have to check each barrel,

Pat

[JBaum]