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Maylaisian 7.62 NATO case seperation in MG42

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Maylaisian 7.62 NATO case seperation in MG42

Postby Waffentag » Sat Apr 14, 2018 6:46 am

I just bought a bunch of Maylaisan 7.62 NATO and had 4 cases separate and get stuck. They separated at the line where the case was annealed. This ammo worked great in my PTR91 and in my friends full auto M14. I gaged it and it is within 7.62 NATO specs, same as other surplus that I have. My reloads run and Australian surplus run without issue. I did notice that the Maylaisian brass is very thin compared to lake city brass?

This happend in three different barrels, I have 7.62 go/no go Gage's and my bolts all gage good with all of my barrels. I have chrome lined barrels in new condition with clean chambers,

I always use a bolt stabilizer, Bob Naess rebuilt my recuperator and put in new springs.

Is it the ammo? Is there something that I can do so that I can shoot this ammo?

Thanks Pat

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby Waffentag » Tue Apr 17, 2018 10:53 am

Any thoughts? Help:)

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby Bil » Tue Apr 17, 2018 1:32 pm

I have not had any luck with this, I stick to the better grade, Roumanian,etc. Don't use ammo from where you wouldn't drink the water, I was always told... :(
"I dream of a world where I can buy alcohol,tobacco and firearms from the same drive-up window,and use them all on the way home from work!" Dogbert

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby JBaum » Tue Apr 17, 2018 9:14 pm

Case separations like that occur because the MG42 shoots so fast, that the case doesn't have time to shrink back down after firing before it is yanked out of the chamber. It'll work fine in other guns because there is more of delay in extraction, so the case, which expands against the chamber of the barrel when fired, is still held against the barrel while it is being pulled out.

H&K based guns use a ribbed chamber to equalize the pressure on the outside of the case sooner so that it extracts easier. Typically, I get 3 shots from a brass case in a 42 before it shows stress marks which indicate it will rupture, split, or the base will tear off if I try to reload it and shoot it one more time. The 42 is hard on brass, and thinner brass is less able to withstand the stress.

Weigh an empty shell and compare it with the weights of other brands. That will tell you what the brass content is. Let us know the details.
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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby Waffentag » Wed Apr 18, 2018 6:35 am

I weighed a couple of cases on my powder scale, the Malaysian came out at 181.1 grains, Lake City came out at 182.1. The Lake City had been reloaded once and I removed the primer pocket crimps, so virgin brass may weigh more.

I will weigh more cases when I get a chance.

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby SturmHead » Wed Apr 18, 2018 2:30 pm

I just bought a can of the Maylaisian ammo. Since I use a MG3 bolt, barrel, feed tray, buffer, and muzzle booster that slows the rate of fire down a bit, I'll have to test John's theory and get back to you. Weather permitting.

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby Waffentag » Wed Apr 18, 2018 7:04 pm

That would be great if you could test it in your MG42. I have the same MG3 setup, everything is German Surplus except my bolt is a yugo, with MG3 bolt stabilizer.

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby Waffentag » Wed Apr 18, 2018 7:57 pm

I weighed a number of the Malaysian cases and they were all over from 180 to 185 grains, the Australian Surplus was pretty consistent at about 180'grains, The Lake City was always about 182.6 grains. Not sure what we can tell from this?

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby SturmHead » Sun Apr 22, 2018 9:36 pm

Okay, I finally got out and shot 200 rounds of the Maylaisian ammo; 1986 lot 2. the first 150 rounds I fired with no issues. The first 50 was in short burst, the second 50 was one burst, and the third 50 was a mix of short and medium burst with no ammo issues. I then changed barrels and tried another 50. About 15 to 20 rounds in I had a case separation. I cleared it, changed back to the other barrel, and fired the rest of the belt with no issues.
While looking for the separated case head, I found a case that had a line around the case and a pin hole in that line, and I believe that case was close to separating when it was fired; I also believe it came from the second barrel, based on where I found it, and before I finished the last belt.
All the barrels used have had the head space checked to that bolt with Foster go/no go Gage's in the past and all showed to be within tolerances. I checked them again when I got home, and the barrel that had no issues did have a shorter head space, than the barrel that had the separation.
I think if your going to shoot Maylaisian ammo your going to need a tight chamber in order to avoid case separations.
While I haven't had a chance to compare the brass with NATO brass, the wall thickness of the brass that separated did look thin to me. But at this point that doesn't mean anything.

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Re: Maylaisian 7.62 NATO case seperation in MG42

Postby Waffentag » Tue Apr 24, 2018 8:10 am

Thanks for testing them out. Here is what bmg17a1, had to say on the gunboards forum.

"Case separations are extremely rare with MG42s in my experience with them.... Since you say that the specs are correct compared to NATO, sounds to me like a combination of thin, brittle metal and improperly annealed cases making them vulnerable to fracture from stress on extraction. Stretching of the cases from loose headspace is a common problem, but with MG42 headspace is very rarely ever too loose with factory barrels with both maker matched and mix-match bolts and barrels, with too tight headspace happening fairly often. I'd suggest trying a couple things: measure the booster orifice and if it is the 9 +/-mm, try a booster cone with a larger orifice. The 11mm is usually standard; lube the ammo in the belts just prior to shooting and see if that helps with extraction.
Lack of elasticity of case metal has never been an issue with M42s in 7.92 or .308 nor in other MGs with considerably higher rates of fire. The rearward travel of the locked bolt and barrel before unlocking is entirely sufficient for barrel pressures to drop to levels allowing for reliable extraction. FWIW"

I was using a 9mm 7.62 German BW 'booster" cone flash hider combo. I will try an 11mm one that I have. I drilled out a spare barrel bushing to 9.9 mm and one to 11.1. I will give them a try this weekend and see if I still get case separation? I also use Foster 7.62 NATO go/no go Gage's, Are they the same dimensions as the German Army BW gauges?


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