MG42 Bolt Body Issue

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MG42 Bolt Body Issue

Postby czerka » Sun Feb 18, 2018 6:31 pm

Can anyone tell me what is going on here. I have had two body bodies crack in the same exact location. Gun is a Post Sample built in 2010 currently set up to shoot the plastic NATO DAG 308 rounds. Both bodies are Yugo, first one survived around 10,000 rnds of 8mm, 308 and the last 4,000 rnds have been DAG. The second only survived around 2,0000 of the DAG rounds. The bolt is currently fitted with an MG3 type bolt catch and a DAG training bolt head also the recuperator was rebuilt by Bob at Black River in 2016. Is this normal, bad castings or is something off in the gun? Any assistance would be greatly appreciated.
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Re: MG42 Bolt Body Issue

Postby Blanksguy » Sun Feb 18, 2018 7:06 pm

As you say that the bolt-carriers were both "Yugo", there is always a possibility that they were bad......but (?) you should check the gun a little closer.

You say a built Post-Sample (with receiver alignment still good-?).......what I am looking at is a bolt-head unlocking on one-side earlier than the other.
If the same Bolt-Heads was used on different bolt-carriers........I would look at that and bolt-rollers......along with close attention to the Cam-Pcs. in the receiver......and......the locking-cutouts in the Barrel-Extension.

When the gun was operating well......were the recoiling parts operating as usual......or speeding up (?).
Going from different types of ammunition sometimes requires the use of different size Booster-Cups.

I'm not sure on the next check........how is the barrel-stop on the inside of the receiver..........and does the barrel-extension have any side-play (left-right) once the barrel and bolt-assembly are both locked and in the forward position (?). Maybe a slight tilt to the right (?).

Last......I've heard some owners use a "Blank" as the last round to keep the bolt from slamming into the Barrel/Barrel-Extension at the end of a belt. Is there any chance that (as "hardened"/brittle parts) the Bolt-Carrier cracked due to this (?).

Regards, RichardS
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Re: MG42 Bolt Body Issue

Postby czerka » Sun Feb 18, 2018 8:17 pm

Thanks for the response Richard. We recently replaced the barrel shroud with an MG3 shroud and the trunnion with a new HK one and I have been concerned that it was not properly aligned. I am using an MG3 booster cup and I am using the DAG muzzle booster which is basically a piston. As far as I know, there is no side to side play in the barrel stop but I will double check when I go back in tomorrow. What I have noticed is when customers are shooting the gun with the DAG rounds the rate of fire is inconsistent it will suddenly slow down and then speed back up and many times when you hear it slow down it will have a feed issue. The cartridge will either take a nose dive and the back end will be sticking up out of the feed tray or it will make into the chamber and get mangled all to hell. None of these issues are present with live ammo and both times the bolt bodies have broken it has been with the DAG ammo. It's being used in an indoor range and because of its rate of fire I am afraid live ammo would put way too much stress on our traps. I like the Idea of the last shot being a blank, I think I will start doing that. Thanks again for the assistance.

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Re: MG42 Bolt Body Issue

Postby Blanksguy » Sun Feb 18, 2018 10:32 pm

When you talk about cartridges "nose-diving" towards the chamber sounds more like the:
1: Cartridge-depressor is bent out of correct "curve".......but:
2: I tend to think it might be more of a recoperator issue where something (piece of dirt/brass/etc. is hanging up the assembly causing the barrel to not move forward as fast as usual........or slowing down....then piece of brass moves out of the way....and the system speeds up.

Question......the alignment (ability of the barrel to move freely without the bolt assembly attached) is not an issue....correct (?).........and the Barrel-Bearing/keys are not hanging up (?).

Regards, RichardS
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Re: MG42 Bolt Body Issue

Postby czerka » Mon Feb 19, 2018 2:32 am

viewtopic.php?f=16&t=13583&p=96621#p96621

Link above is an example of what it is doing, it is a pic of my 34 from a previous but same exact issue. It's kinda funny because I was referred to you for that problem, just saw the response today but I kinda gave up on that issue. On the 42 issue, what do you mean by move freely? Freely against the recuperator, then yes if I push on the bearing the barrel moves in and returns to position. I will do the pogo test on it tomorrow just to see. I checked the recuperator yesterday and it seems to be working fine I pushed it in by hand using a screwdriver didn't feel any binding. I cleaned the recuperator a couple of months ago, My method of cleaning it has been washing it thoroughly with hot water and degreaser then blowing it out with an air compressor then lubing it good and using compressed air to force the oil down into it. Do I need to fully disassemble to clean it? Really have not wanted to go down that road. Also how often should it be cleaned? So far issues have not occurred with brass or steel cased ammo but I do not run live ammo through it very often. The rate of fire with live ammo is considerably higher as well. While the plastic stuff cycles between 900-1000 rpm live ammo is around 1300 rpm and with live ammo the rate of fire does not speed up are slow down but it may be just running so fast I can't detect a change.

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Re: MG42 Bolt Body Issue

Postby czerka » Mon Feb 19, 2018 12:18 pm

I think I just discovered the issue, it is the DAG muzzle device. When I screw it all the way on I noticed it pushes the barrel back about a quarter of an inch so the barrel is not able to fully extend during operation. Attaching an MG3 flasher hider does not do this. I think this explains why I am only getting this issue with the DAG rounds. I am going to try screwing it down until the piston just makes contact with the bearing and run a belt through and see if the problem goes away.

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Re: MG42 Bolt Body Issue

Postby Jaredrlewman » Mon Feb 19, 2018 12:29 pm

czerka wrote:I think I just discovered the issue, it is the DAG muzzle device. When I screw it all the way on I noticed it pushes the barrel back about a quarter of an inch so the barrel is not able to fully extend during operation. Attaching an MG3 flasher hider does not do this. I think this explains why I am only getting this issue with the DAG rounds. I am going to try screwing it down until the piston just makes contact with the bearing and run a belt through and see if the problem goes away.




The DAG booster is adjustable. You take it apart and put the main portion on the gun until it is tight. Then put the internal piece in and screw the outside cup on until it pushes your barrel then back off to the next notch and lock that piece down. You are getting OOB explosions there basically, luckily that stuff doesnt have a ton of @ss behind it..


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