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MG34 runaway


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Hi all. I have two MG34 premay dealer samples. The most recent one I've acquired had an ejection problem which I sorted by installing a new ejector plate as the one on it was heavily worn. It's running great now, but a little too great! I can't figure out why I'm getting runaways on it. Function test works fine. I've changed out bolts, put a new sear, sear spring and sear lifter. I've disassembled and inspected all trigger components and even tried a completely different trigger assembly. I've tried a new main spring and two different others that were lesser in length but still within spec. I'm thinking based on what little I could find from searching here that the timing may be off. I have a long, long as in the longest recuperator spring I have in right now. I have others of varying lengths that I may try next but I just can't wrap my brain around how timing could cause it to run away because the bolt still has to come back over the sear unless it's short stroking which may be the case. Please chime in with thoughts or suggestions. Thanks in advance.

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Looking over at all you described, that sear/finger that sticks up from the trigger group, which drops down out of the way when you pull the trigger and releases the bolt to go forward, has to be the offending piece......in not popping back up to grab/block the bolt from going forward in it's cycle.....

….I had a similar problem with my 1934 made MG-34, and the problem was in the trigger group......It amounted to a pin that the crazy sear assembly rocked on...> the pin was not set in all the way, bridging across both walls of the assembly (upper of grip), which allowed the sear to not be solid and gave way when the bolt was supposed to be stopped by it sticking up. Oh, the bolt would stay cocked when I cycled the gun by hand, but ran away when shooting!

….Mr. Rebel, I hope this makes sense, ha!, ...This happened to two trigger groups that I have, one on gun the other on dummy gun...

...I found a way to keep that pin all the way in by placing a rubber spacer between the head of the pin and the inside of the plastic grip.(used the rubber of No.2 pencil eraser)…..

…..I was so frustrated, but fearful to take that grip apart, but then, JOHN BAUM came out with a translated manual of the MG-34 Trigger Grip, only.....devoted to the grip, and then I really got into the many nutty parts of this grip!...….(hello Mr. Glock, who was a MG-34 gunner at the end of WWII, & was influenced by this crazy ass trigger in his gun of the future)

…...I would suggest getting this MG-34 Trigger grip manual from John..> It has COLOR diagrams that will help understand this over-engineered trigger group!

...I was determined to keep my $30,000. gun from remaining a run away gun. I had to find the problem!!...bobh

 

 

Ask John Baum for his , "The MG-34 Trigger System".....manual. :)

 

 

 

 

 

 

 

…..

Edited by junglewalk
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Hi Junglewalk. I have read your response several times and disassembled my trigger group to inspect the trip. My pin is solid and hasn't walked out. I also have another MG34 trigger group. Both trigger groups won't work on one but will on the other so I'm thinking it may be a timing issue where the bolt is being short stroked. However, I'm not opposed to the fact that it could still be the trigger groups just not working in one of the MG's. I'd like to get this book. How do I find John Baum?

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RRO, had mg42 with a similar problem. The problem was the recoil buffer in the stock. Can’t give exact measurements as don’t have gun any more. When the gun is cocked how much space is there between rear of bolt and buffer spring that bolt recoils against.If it’s about 1/8 “ it should be more like a 1/4 “ What happens is the bolt does not come back far enough for the sear to pop up to catch the bolt. It needs slightly more travel so the sear can pop up. Had to knock pin out of the large screw that goes into bolt recoil buffer spring. Turn screw a half Turn ? or more to get correct space. Then drill a new hole to replace pin which locks adjustment. Maybe some current owners of 34 s or 42 s can give you measurement of space between bolt and recoil buffer on their guns. Something to check. Again when cocked you should be able to pull bolt back about a 1/4 “. HTH. M17 ap
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OK, I was hoping my solution would be able to help....> John Baum is at https://www.germanmanuals.com/>

...John will answer you pretty quick, and you will be impressed with his long list of German Manuals that he translates into English, and then prints the manual in English with copies of the original diagrams and photos......He also sets up here at Knob Creek Rg for the Machine Gun shoots on the Allegheny Arsenal table, and at gun shows. :)

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RRO, had mg42 with a similar problem. The problem was the recoil buffer in the stock. Can’t give exact measurements as don’t have gun any more. When the gun is cocked how much space is there between rear of bolt and buffer spring that bolt recoils against.If it’s about 1/8 “ it should be more like a 1/4 “ What happens is the bolt does not come back far enough for the sear to pop up to catch the bolt. It needs slightly more travel so the sear can pop up. Had to knock pin out of the large screw that goes into bolt recoil buffer spring. Turn screw a half Turn ? or more to get correct space. Then drill a new hole to replace pin which locks adjustment. Maybe some current owners of 34 s or 42 s can give you measurement of space between bolt and recoil buffer on their guns. Something to check. Again when cocked you should be able to pull bolt back about a 1/4 “. HTH. M17 ap

 

Did some checking. 34 & 42 recoil buffers are not the same. 42 has screw where 34 has a tube with a cap to hold recoil buffer and spring inside. I guess on this model you may need to shorten ( machine off some metal ) from the recoil bushing , or spring itself. Or find a shorter bushing or a used compressed spring. Sorry for mistake. I did the above modification on the 42 I had and it corrected my run away problem. M17ap

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  • 4 months later...

I read in the MG34/MG42 by Folke that the MG42 can become a runaway gun due to a weak sear spring. It stated that it can allow the sear to start to vibrate when hit by the rear edge of the sear bent. I'm not sure if this would translate to your problem on the MG34.

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I read in the MG34/MG42 by Folke that the MG42 can become a runaway gun due to a weak sear spring. It stated that it can allow the sear to start to vibrate when hit by the rear edge of the sear bent. I'm not sure if this would translate to your problem on the MG34.

 

True enough, I have that book as well. The cause of mine was actually the sear itself. The sear I had in was NOS but must have been out of spec or made on a Friday late in the war. Put a different sear in and the problem was solved.

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