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Bolt Catch


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#1 Armydoc0115

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Posted 24 July 2018 - 04:51 PM

Alright, guys....hoping someone can clear something up for me about bolt catches.

Everyone says don't risk barrel bounce by firing without a bolt catch.  OK, got it.  Even the Germans apparently recognized and researched the problem in the 1940s.  My question is whether the bolt catch was designed during or after the war?

There are apparently three different bolt catches, with one being the version used in the modern MG3.  Of the other two, I understand the first version of the bolt catch was made by Mauser in 1944, was longer and is really hard to find.  But then on reading Chris McNabs book on MG 34s and 42s, he says "Incidents of 'bolt bounce' were noted, and resulted in some catastrophic gun failures, and the problem wasn't really remedied (as far as we know) until after the war."  That, of course, makes it sound like bolt catches were a post-war improvement.  So which is it?  Did the Germans create the bolt catch during the war, or did it come about post-war?

Thanks.  


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#2 johnsonlmg41

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Posted 24 July 2018 - 07:35 PM

Primarily post war and mostly an ammo issue.  I've run without them but I don't run the guns that much and I can't say I'd recommend it, but the guns were run most of the war without them.  They all ran pretty well with German ammo tailored for the gun.  Post war ammo from different countries is significantly different than WWII German MG ammo and thus it was probably imperative it be added if they ever wanted to sell the guns commercially.  I'm still running the '39 stuff and haven't broke into the "new" stuff yet.  There are still a lot of German metallurgy that hasn't been duplicated even today and still remains a mystery.  Folke's book has a bunch of info on it but I don't recall most of the details and am too lazy to grab them off the shelf.


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#3 Black River Militaria CII

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Posted 25 July 2018 - 04:51 PM

The issue out-of-battery ignitions in MG42s is a fascinating story. MG42s were plagued with this problem all through the war. The cause was eventually revealed and analyzed by high speed photography of the action which showed that the rollers oscillate as much as 1mm out and in when lock up is proceeding and then they settle into lock. The barrel must return to full rest in preparation for the next round in the extremely short interval between shots and given that the gun is capable of 1200 rpm, this is not much time. However, if the ignition occurs when the rollers were in the outer position of the oscillation, an OTB could, but did not always occur. Apparently enough guns were damaged and put out of action for repair or lost to warrant finding a sloution. Once the problem was identified, the solution was to design and manufacture ammo with primers with a slightly slower ignition time which allowed the rollers to settle into lockup and issue that ammo the specifically for use in the 42s. This was a temporary cure for the problem. The bolt catches were not used during the war and were a post-war development. There are five variations of the catches.
There are other wear issues even with the bolt catch in place that can facilitate an OTB ignition. This can be a problem with the barrel return recuperator. If the springs are broken, or have taken a set or are compromised and are not fully capable of returning the barrel to rest in the very short interval between shots, the damaged recuperator can facilitate an OTB ignition. If left without replacement the problem can result in damage and eventually chipping and fracture of the ends of the trunnion (curved piece which contains the locking ramps) unlocking cams requiring replacement of not only the recuperator sptrings but the complete trunnion.
Years ago before the need for the bolt catches was well known, OTB ignitions happened enough to scare owners. The catches were purchased and installed. I had quite a few MG42s through my shop at one time damaged by OTBs, but havent such type of damage now.
As Jeff notes above, rifle ammo was used during the war until special ammo was provided to the troops for the MG42s and recreational shooters were also using rifle ammo which does require the use of a catch.
Any variation of a bolt catch will suffice for use in the bolt of a 42. Dont shoot a transferable wihout one.
I had a 42 in the shop where the extractor punched a hole right through the bottom of the receiver. Lown out by an OTB ignition. Might also have been defective ammo, but it was impressive nonetheless. FWIW

Edited by Black River Militaria CII, 26 July 2018 - 07:38 AM.

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#4 michaelkih

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Posted 01 August 2018 - 05:02 AM

Slightly off topic, but as Bob says above, the timing has to be perfect for these guns to safely run.  If you get one or have one, I would highly recommend sending it to him so he can replace your recuperator spring and look things over.  He took care of my MG42, and I could not be happier with the results.  Runs awesome!


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