Pierced primers and light strikes?

[mt4x4]

This weekend I put about 120 rounds threw my post MG42. I have had plenty of problems with this gun and most of them have all been worked out. During the 120 rounds I had a few rounds that did not fire due to light primer strike. I found about 10 or 15 cases that had pierced primers. All the other cases seemed normal to me. They had much deeper primer strikes than my rem 700 puts in them but I think that is normal. This gun is running 308 with the 2 part booster/flash hider used for 8mm. It runs at about 960 rounds per min using the 11 booster with the longer barrel bearing that came with the 308 kit. The ammo is the CBC Magtech stuff I picked up maybe 6 months ago. I’m using a mg42 bolt setup with anti-bounce parts installed the correct way. The gun does the pogo test just fine. I swapped barrels halfway through and that did not fix the problem. Both barrels headspace just fine. Fine as in it just barely closes on a 308 no-go with no force required and not even close to closing on a 308 field.

It jammed maybe 2 times with nothing in the chamber. I think this was due to the belt getting tangled on the table. A quick charge was all it took to get going. I will try to get pics of the cases tonight but in the meantime does anyone have any ideas why some cases had light strikes well others had pierced primers?

[42rocker]

Have a semi-auto so can't help much.
But can say glad to hear that you have it running at least. Almost all (almost) of these type of problems that I have read about in full auto are caused by ammo problems. Not knowing anything about your ammo and a lot of full auto stuff I would say wait till some of the other members see this post and chime in.

Later 42rocker

[K98dkmauser]

do you have another fireing pin?

[crash520]

MT,
your light strikes will more than likely be the pieces of primer that have blown up past your firing pin when you suffered 'pierced' primers, we see this alot in bolt guns with hot loads once you blow a couple of primers the pieces of primer that have blown back through your firing pin hole start to impeed on your firing pins ability to move freely thus causing missfires.

As for Pierced primers, I wont get into that as I have my views, suffice to say certainly look at firing pin protrusion, firing pin hole diameter, hot rounds.

VR
C

[42rocker]

Those sound like good ideas to check out.
Thanks

Later 42rocker

[mt4x4]

Thanks for the help. Sorry for the delay I have been out of town. Maybe tonight I will get a chance to get the pics up. I do have an extra firing pin but if I remember right it would not fit. I think the diameter is too big. I may pick up a few extra next order at rtg.

[JBaum]

If there's a problem with firing pin size, there may actually be a problem with the firing pin hole size. I'd try another bolt head too.

[robertmcw]

Look at you booster. Clean the inside of the bolt and the fire pin and crank the booster LESS, two or three threads, and report back.

Robert

[mt4x4]

I was just thinking about that. Now that I think about it this gun is shooting 960rpm with an 11mm booster I have a 10mm booster but the gun would not run as I think it was trying to go to fast. I think you meant for me to crank the flash hider less. If this is my problem I think I could shorten up my Barrel Bearing just a bit as a permanent fix. Been busy working so I hope to go out this weekend and test.

[robertmcw]

I have working about 9 years on my MG42 SEMI and it has always pierced the primers. I read here that the booster may too smug to the receiver. I backed the bushing to about half of the threads on the bushing and shot and it seems to have stopped the issue. Now I shot only it three rounds but all three primers were not pierced. I plan to shoot more later in the week but if that if I can get 100 rounds with a 100 with intact primers, we will assume that was the problem.

As expensive as ammo is today, every round counts.

One post here said to back the booster all the way and shoot it (remove it). The brass should not eject. Remove the spent round and twist the booster a couple times and do it again. You will know when the booster is in the right place when it works. Keeping shooting and twisting until the round gets pierced the and you can know where the sweet spot is – between where it works and where it fails.

[JBaum]

I find it interesting to see people suggest that the MG42 recoil booster is somehow made to be adjustable. It is not.
REPEAT: It is NOT adjustable.

The German MG42 manuals say that the booster/flash hider is screwed on until tight, and only backed off enough to get the detent lever to drop into a slot. I would think the Germans should know how the gun is to be operated and have the correct information in the operating manuals that they issued to the people who carried it in combat.

Shorten the barrel bearing to permanently fix a problem? Do you cut down the tires on your car because the speedometer is off? Maybe take out a piston if the car is too fast?

I'm amazed that people who have a gun worth thousands of dollars, and if on a Form 4, worth tens of thousands, don't read the operating manuals for it, and then even pass along incorrect information. Making your choice of reading material on an expensive gun based on reading the only manual you can find that's free, is, in short, getting what you pay for.

Anyone who has read the U.S. WWII manuals for the MG 34 and MG42 needs to realize the old U.S. manuals for the 34 and 42 are pieces of crap with incorrect information in them, written by people who didn't know how the guns worked. These same types of people are still writing crap U.S. government manuals for foreign guns. Free doesn't make the information correct. You guys spend a lot of money and time building a gun, then rely on misinformation (because it's free) to learn how to run it, and pass along totally wrong information as though it is fact. Scary. The U.S. manual is the only thing I've ever seen that said to "adjust" the recoil booster. It is an incorrect suggestion.

1. If you have excessive recoil, the solution is to use a nozzle with a larger hole. This isn't a Bren with a variable gas system.

2. Excessive recoil does not cause irregular primer strikes. The first thing to do if this happens is to change the bolt. If the problem goes away, you've found the cause. New MG3 bolts are available for very reasonable money, and are valid for use for 8mm and .308. They cost much less than the time you'll waste patching the blown receiver.

I don't take my 42 shooting without at least 3 bolts along, and a few barrels. Also, shooting a 70 year old MG42 bolt that was made while the guys worried about being bombed is nuts. Have you ever seen crystalized steel shatter to splinters? Was the heat treating right? Was slave labor at the controls when it was made? At 25 shots a second, this isn't the place to be cheap.

And don't even suggest that I'm on a rant because I'm trying to sell a manual. I always answer any question I can, and explain the information from the manuals without hesitation to anyone who asks a question. Been doing it here for years, and do it at Knob Creek for people who don't want to buy anything, but are just looking for free information for their $2,000+ post-sample gun, or $35,000 transferable gun. I've never asked for a dime from them for explaining their 42 to them, nor have I told them to buy a manual. Glad to help out, but it's disappointing to see the danger people put themselves in by not knowing anything more than how to weld. Some of these people should have stuck with building dune buggies with pipe frames.

I don't want to see people get hurt or have problems through ignorance. It makes us all look like fools, when most of us are not. I don't know everything there is to know about the 34 or 42, but I've read 20 German operating and repair manuals in two languages about them. I trust that the Germans knew that what they were telling their men was correct information.

Rant over, I feel better now. I'll return this thread back to the original participants.

[42rocker]

And Thank You John for those kind words. Rant over. LOL.

You always give us (ok, me at least) interesting things to think about. Now it's morning John go have and have some more coffee.

Later 42rocker

[robertmcw]

John,

I did not mean to step on your toes – after you are the expert not me.

And I shot it with the booster tight all the way BUT I changed the SEMI springs from RTG and a new firing pin and spring and now all is well.

Now to get some anti-walk pins……..

Robert

[JBaum]

No toes of mine were stepped on, no hard feelings to/from anybody.

I wasn't in a good humor to start with, and just vented a little when I read about adjusting the booster, because I now know where the idea that the booster is adjustable originates. Repeat any lie long enough and it starts being believed as truth. We (gun people) are on the edge of being tolerated now. We don't need to call attention to ourselves by having accidents.

The booster isn't adjustable, and the MG42 does not have a trunnion. The M60 has a trunnion. The MG42 has a cam piece. I'm OK (twitch, blink-blink) now.

The only reason I know about the 42 is because I've read the real manuals, and I just get torqued when people read the US manuals and believe them. Something dumb can happen too easily with guns, and bad information just makes it that much more likely to happen. I don't want to read online about "those crazy gun people" doing stupid things that make people go to hospitals (or morgues). A rant once in a while is very soothing, after it's over. For me, anyway.

[42rocker]

Ok, John easy now that was your TWO THOUSAND and FOUR HUNDREDTH post. Take it easy now. Interesting to think about how most of your posts have been posts trying to help other folks out with their mg42's and other weapons.
I personally say Thanks for all of your help, even on the rant days. LOL.
Have a great weekend everyone.

Later 42rocker

[mt4x4]

Thanks John. I at least owe you lunch for all your help. I found that unscrewing the flash hider half a turn did not make any difference as john knew. However I did look threw my parts and found another Striker Sleeve that was smaller than the one in my bolt. After swapping my problem went away. I will include a picture of the brass.
My thinking on the barrel bearing is I have another one that makes the gun shoot so slow it won’t cycle. In my observation to short makes the gun shoot too slow and too long makes it shoot too fast. If I had one somewhere in the middle that should be just right. How else should I go about getting my gun to shoot 900rpm with a 10mm booster? Anyways it worked without a problem for at least 100 rounds other than I had the top pop open.

[JBaum]

I like it when it works. Spare bolts are mandatory, at least for troubleshooting a problem.

The long/short variations of barrel bearings is something I'm not familiar with. I think that stuff came along with the M53. I'll tell you what I know, and I'll tell you what I don't know. Don't know about barrel bearings.

I will say that .308 has a lower rate of fire than 8 mm Mauser, all other things being equal. On my 42, I don't change the nozzle when I switch from 8mm to .308. Runs fine with either caliber, just a little slower with .308.

[mt4x4]

Is the top popping open normal?

[42rocker]

No. Weld length might be off. Or wear or bent or ?

Later 42rocker

[gordie k]

John know you know why i don"t post
gordie k