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MG34 Semi auto bolt jamming

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radar617
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MG34 Semi auto bolt jamming

Postby radar617 » Sat Jul 11, 2015 2:00 pm

Hello everyone,
I recently purchased a home build semi auto MG34 that was having jamming issues. Its a reweld receiver and early TNW trigger with one roller. If you rack the MG it cycles fine, it passes the drop test, and I have done a good amount of polishing. At first when function checking with trigger pulled it jammed half way when bringing to the rear. After lots of polishing on the bolt and metal around where the trigger arm folds back into the receiver, the bolt hangs up in the rear position (about 99% to the most rearward position). The bolt seems to be hanging on the trigger arm. The only way to clear the jam is to pull on the charging handle and pull the bolt back about 1/10 of an inch and then the trigger resets and the bolt is free. Does anyone have any further ideas or should I just keep polishing?
Thanks in advance,
Jason

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Re: MG34 Semi auto bolt jamming

Postby anjongni » Sun Jul 19, 2015 4:02 pm

Hi Radar, just noticed your post.
If you haven't got it running yet, you might actually take a look at the ejector, the little pin atop the right side of the bolt head, while you're hand cycling the weapon.
If the ejector in in the "rearward" position as the bolt moves forward, it can catch on the ejector plate as the bolt drives ahead, jamming the bolt. Cycling it slowly, or cocking back allows it to pass, once.
This seems to be an issue of individual bolts coupled to different receivers. I have several different bolts, and all the ejectors seem to be matched, or have worn themselves to match, their respective receiver/ejector plate combo.
And maybe just semis. Maybe the full-autos set up such severe vibration that the problem couldn't occur.

I had TNW convert my trigger and install the two rollers. It wasn't expensive. Would that be an upgrade to smooth out the system? Well, good luck with it......Phil

radar617
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Re: MG34 Semi auto bolt jamming

Postby radar617 » Wed Aug 05, 2015 8:55 am

I've looked at the ejector pretty closely and doesn't appear to be the problem. Without the trigger held down I can rack the bolt all day without it getting stuck. I retook another look at just about every part in the area and I've come to two ideas. Either the trigger is being pulled too far back jamming the trigger arm against the bolt or the trigger return spring isn't the right one/too weak. The trigger return spring is several inches long and its twisted behind the trigger. Looks like someone just tossed what ever they had laying around. Good news is after polishing away at the trigger arm and bottom of the bolt I got it where it jams on the return and about 2" from being fully locked up. Almost there.

Blanksguy
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Re: MG34 Semi auto bolt jamming

Postby Blanksguy » Wed Aug 05, 2015 2:39 pm

When MG34 new Ejector-Pins (part of the Bolt-Assembly) are fitted to a Bolt-Head, they are sometimes required to be trimmed on the end of the pin that makes contact with the Ejector-Plate.
This is done due to excess material dragging inside the receiver when a cartridge is mounted in the Bolt-Face......which pushes the ejector-pin upward for contact with the Ejector-Plate during recoil........and that some pins/MG34s are just slightly too long.

Have you cheched to insure that the ejector-pin is not too long...........it would show up as working good/no drag when gun doesn't have a cartridge on the Bolt-Face......and then dragging/hard to pull bolt back after a cartridge is attached to the bolt-face. (?).

Regards, RichardS
US Army, Retired

messerschmittfan
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Re: MG34 Semi auto bolt jamming

Postby messerschmittfan » Wed Aug 05, 2015 8:41 pm

You might want to go to the TNW dual roller as that is one of the reasons why they did, the single roller will sometimes allow the trigger bar to tilt and hit bottom of bolt. Easy modification to add the extra roller. Now if I could get the length of the trigger pull solved. Harry


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