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Do you need to head space a tnw SA MG-34 when you put in a new barrel or bolt?

Headspace should be checked on all bolt/barrel combinations that would be used. One barrel might have the chamber a bit deep, although still within tolerances, and a bolt may be a bit loose, although still within tolerances. The combination may combine to an excessive headspace, or if the reverse situation is true, it may be a bit too tight.

For my MG42, I have one bolt/barrel combination that's too tight. All other combinations are OK. I have marked that one barrel as not to be used with that one particular bolt. Eventually I expect that the barrel may wear enough to allow that bolt to be used with it.

When i called TNW, they said there wasnt a headspace for the MG34. Is this the case? I would assume since the barrels would be changed when hot, you couldnt sit and check headspace every time?

They should be headspaced. That is why barrels were numbered. They were checked before hand so there would not be any problems. This kept it easy in battle to have 3 or 4 barrels and 2 or 3 bolts ready to use in any combination.

I had TNW convert an extra bolt for my 34, asked them if they wanted me to send both barrels to check headspace with both barrel & bolt combinations and they said it wasn't necessary.. Figured I'll check it myself whenever I switch out the original pair.

Roger from Iowa

While the MG34 headspace is not adjustable, considering the quality of some of the barrels that are around, it's wise to check it to see if it is within tolerances. The MG42 headspace is not adjustable either, and I've seen wide variations in headspace, with one gun blowing up because it was too tight.

Trusting that all is well when it comes to swapping out parts is like being the pilot and trusting the air traffic controller that there's nothing coming. You check anyway, because a controller was never killed in an airplane collision.