Maylaisian 7.62 NATO case seperation in MG42

[Waffentag]

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

[Waffentag]

Any thoughts? Help:)

[Bil]

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...

[JBaum]

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.

[Waffentag]

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.

[SturmHead]

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.

[Waffentag]

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.

[Waffentag]

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?

[SturmHead]

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.

[Waffentag]

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?

[SturmHead]

Don't know about Foster vs. German gauges.
I would like to know what your results are with the different booster diameters.

Just remembering back, it seemed like when I first got the 42 in 8mm, it ran with no issues even though all of the barrels I had would lock on the no go gauge, and I ran all kinds of 8mm through it. Changed over to 7.62 NATO and had good luck starting out. Now it seems like head space and ammo quality are critical.

How does the Wolf steel cased 8mm run in the 42?

[Waffentag]

I will not be able to make it to the range this weekend, but will let you know when I do get to the range.

8mm seemed to run fine, I have not tried the wolf, I was using some FN made stuff.

The 80s steel Romanian surplus seemed to run fine in my 08/15.

[Waffentag]

This past weekend I went for one day to the Shooters Gauntlet MG Shoot, Stone Mountain, in PA. It is a smaller mini Knob Creek. Great Fun, they had five cars, a "tree cutting contest'. I did not have a chance to test Bobs recommendations prior to the shoot. I put in a booster cone with a larger orifice and I lubed the ammo in the belts just prior to shooting. At first it shot OK, then I was having light primer strikes and jams. I assumed that it was the larger booster hole. But in retrospect it could have been a number of things. I was using some brand new HK21 belts. This style belt had worked fine before. I had placed a small piece of rubber on the trigger guard to keep case necks from getting crushed. Perhaps the cases were hitting the rubber an bouncing back into the ejection port. At the time, I read this to be a failure to eject. During the day, I swapped back to a smaller booster hole, I changed barrels, bolts and recoil springs. To be frank, what I did and when I did it is all a blur now. This type of shooting event is not conducive to clear thinking and methodical trouble shooting.

By the end of the day, I had shot 2000 rounds, had numerous malfunctions which never occurred before and 5 cases separate. At least one case was new Factory Lake City and the others were Malaysian, This time, three were pulled off at the very base of the case. I saw other brass with signs of almost separating., One more toward the shoulder. Two stuck in the barrel, the others were pulled out when I ejected the next round that went partially into the chamber. I went to the range with 5 barrels and 5 bolts and used all barrels and three bolts.

When I got home, I retested all barrel and bolt combinations with my 7.62 Min and Max Gages. Two barrels had some bolts that closed on the Max gauge. One these barrels was one that came home with a stuck case. I had one barrel with a stuck case that gaged good with all bolts? Strange, I had tested all 5 barrels with all 5 bolts prior? Maybe I messed up?At home, I pulled the gun apart for detailed cleaning and inspection and noticed a couple of things. The nut that hold the recuperator that sits under the grip was loose. I noticed that the buffer section that the buffer spring sit over needed to be tightened back down into the buffer.

So, to keep things straight on the range, I tested and marked 3 barrels and 5 bolts with a tan paint stripe. All five bolts were tested as good in all three barrels. I found another bolt head that is good with the other two barrels and painted a red stipe on those. I decided just to swap out everything with spare parts that I had before doing some more methodical testing taking my time at my local range. I put in a new grip stick, a new buffer, spring and stock, new charging handle.

I will start with known good belts and LC, and tested barrels, if that works, I will test the Malaysian Ammo. I will go through testing all barrels and bolts, and go to larger boosters if needed? I am not sure what else to do? Any advice is appreciated.

[SturmHead]

Junglewalk and I are going to get together in a few weeks and work on a few issues. One of them is going to be the Maylaisian ammo issue. I'll post results if I survive.

[Waffentag]

I shot the MG42 today. Three barrel bolt combinations fired a number of Malaysian 7.62 without case seperation. Two barrel bolt combinations tore the Malaysian cases in half? Also had a Lake City case seperation. These barrel bolt combinations gaged good? Not sure what is going on with these two barrels? They are in West German Chrome lined and new condition.

Oh well, I have five 7.62 Barrels, I just won't use these two. Since these barrels gaged good, I am not sure that trying another bolt would work?

I had another problem with an FTF, light primer strikes. I swapped out the main spring and solved that problem

[JBaum]

Barrels get the headspace checked with each bolt. Check each barrel with every bolt you have. Is that what you did?

[Waffentag]

John, Roger that, all bolts were tested with all barrels and marked.

Yet, still two barrels that tested good with the bolts that I was using had case separation with both Malaysian and Lake City???

I have 5 barrels and more than 10 bolts, and a 7.62 NATO case Gage. I have read the manuals, both yours and the original in German.

I thought it may just be an inconsistent lot of Malaysian ammo, but then Lake City too? What is really strange, it does not happen with my reloads using LC Brass.

With all combinations that I used, tested good with the Gage, it does not make sense, that two barrels are causing trouble with multiple bolts? Also, changing booster size from 9mm to 11mm did not make difference before?

At least I have it down to two problem barrels, I can try live fire with my other spare bolts and maybe try a larger booster with these two barrels for these two problem barrels

But most shhoting sessions, I am more than good with three barrels.

[JBaum]

I'd suggest cleaning the chamber of one of the problem barrels. Put a stainless steel bore brush on a rod, put the rod in an electric drill, and run it in and out for 30 seconds or so while squirting some bore cleaner on it. The shell might be sticking in the chamber causing it to pull apart.

I had to do that once with a friend's AR15. It solved the guy's problem permanently. He had been having fail to extracts for weeks until I buffed it.

[Waffentag]

Thanks John, I will try that. I did a use a bronze brush on a drill bit prior to shooting. The chambers are chrome lined and really shine, so I was not as concerned.

I will try what you described and see if it solves the problem.

Pat

[amafrank]

Over the years of shooting Full auto MG42s we had a lot of issues pop up. Case head separations did occur but not very often. When it did occur it was normally an ammo related issue and something that would happen in a particular barrel and not necessarily others. From your original post it sounds like your separations are happening just below the shoulder of the case.....where the annealing ends I think you said. This is not always due to headspace. Headspace related separations normally happen just forward of the case head where the case is unsupported. Failures of that type can be pretty hard on guns and with the MG42 often result in the barrel door being blown open and/or bent. We used to have a lot of problems with french made 8mm doing just that and as a consequence quit shooting it in the 42.

Failures of the case further up toward the shoulder usually mean the cases are weak, as Bob noted-brittle, or that you have something causing the cases to stick to the forward part of the chamber. Normal operation of most semi or full auto firearms have the cartridge case pushing the bolt back and not yanking of the case from the chamber. The residual pressure inside the bore is what operates the cycle though most folks seem to think its the bolt pulling the case free. When things are working properly the case shrinks away from the chamber walls when the pressure drops below a threshold point and are then free to slide out. There is still enough pressure to push the case out when the system unlocks. In gas boosted recoil systems like the MG34 and MG42 the pressure has already dropped below the bursting pressure of the case when the action unlocks. The residual pressure continues to push/accelrate the bolt back and inertia/momentum insures there is enough energy to finish the cycle. If the case is stuck in the chamber the already imparted inertia may yank the case free or it may not. If the case or part of it is stuck to the chamber wall it may pull the free portion out of the chamber breaking it off the stuck part. If your cases are breaking inside the chamber rather than the space between chamber and bolt face then it is most likely that this is your issue and not headspace.

A lot of things can cause sticking. Brass can flow into flaws or imperfections in the chamber wall and mechanically stick to it. Use a borescope to look in the chamber for these imperfections. They can be microscopic or huge. Brass that is too soft is more likely to stick. With barrels made in wartime you can find some with rings/grooves made by swarf or damage to the reamer used to cut the chamber. In barrels where the chamber was hammer forged it can happen when debris gets between the mandrel and the blank as the hammers run.
Brass can weld to the chamber wall if things are clean enough. Other chemicals can cause sticking as well or enhance the "brazing". A clean chamber is a happy chamber but I'm not one who would condone the stainless cleaning brush in a drill trick. It can be a cause of sticking as much as a cure. You can have the chamber too clean and stainless brushes can score the walls of a steel chamber. Build up of other materials in the chamber can create a sticking problem too. We are looking at normal working pressures of 50-60 thousand psi and temperatures of 2-4 thousand deg F. In reality its a miracle that the guns work at all.

We found in our collection of barrels some years ago one 8mm barrel that would work fine til it got hot and then start having extraction issues. At the time I had a friend who did precision measuring with lasers for laboratory stuff. He checked out the chamber and found that the front end of the chamber was larger than the rear and as it heated the difference grew greater. When we ran out of the steel cased surplus we had been shooting the brass cased ammo started having issues.....now we knew why.

There can be many causes for your problem and headspace is the least likely. Ammo is high up on the list but if you're having the same issues with other ammo then its most likely your barrel. One other thing could be the recuperator. If the springs are broken or weak things could be happening sooner so that unlocking is occurring before it should or that timing is off. Bob Naess has had springs made to replace the originals with a newer type. In the 2 MG42's I had years back the replacement of the recuperator springs fixed all the ills that one gun had and allowed me to run both on a twin mount where they wouldn't before. Prior to replacement the gun needed a 9mm booster cone hole to run at all. After replacement it would run reliably with a 14mm cone from an 8mm setup.

Some ammo will have problems regardless of what you do. In the 80s we tried tightening headspace to cure the problems we were having. Using US made 8 mauser gauges I trimmed the flanges on the barrels so they would screw into the extensions further to tighten headspace to the go spec. All it did in the long run was make the gun less reliable. The ammo that had separations still had separations with no change in frequency. The ammo that worked still worked but we had more frequent failures to feed or fire. With the original barrel/bolt combos we found the headspace was frequently larger than the gauge specs but we had no problem with separations. So my recommendation is that you check your chambers in barrels that have issues. Check your ammo and be very careful with scrubbing things. You may have a short term cure and a long term problem.

Frank