How safe is a welded receiver?

[Blitzkrieg70]

I have a few questions about a rewelded MG 34 receiver.

Is it safe to shoot?

Will the temper or hardness of the metal be compromised or weakened when the receiver is rewelded?

Will the changed tolerances (+ or - ) cause premature wear of bolt or internal parts?

Is there any way to reheat treat or temper the receiver?

Can anyone recommend an individual that has experience in rewelding a receiver?

What would be an estimated cost to have this work done?

[Johnny Peppers]

At one time the U.S. military was decommissioning (destroying) M1 Rifles by torch cutting them through the middle of the receiver. There was no large source of M1 Rifles at that time, and enterprising businessmen bought the receivers for scrap. They found two pieces that were long enough to cut and weld together and machine back to original dimensions. I have no idea if they re-heat treated them, but never heard of a safety problem. The critical area of the receiver is the locking lug area, and the rest primarily just holds everything in alignment.

[bmg17a1]

First, MG34 receivers are not hardened or heat treated, as no purpose is served for the time and expense for the labor and extra cost of the alloys and production processing required. Having welded together many receivers for many different MGs, including MG 34 receivers, I have found the MG34 receiver alloy to be readily
weldable with an appropriate filler rod and no undue hardening of the receiver alloy from the process. If brittleness occurs, the welds can easily be annealed.
Second, it is unlikely that a weld would fully fracture and open up suddenly on a welded receiver. If the weld does fail and a crack suddenly develops and opens up, the separated parts of the flexing receiver will interfere with the internal alignment of the receiver and the bolt or bolt/oprod will bind and no longer function.
The main stress on the receiver, generally, is the impact of the bolt or oprod/bolt assembly on the rear of the receiver. Some MGs have little buffering and higher impact on the rear of the driver. Individual types of MGs would present unique issues with welding the receiver together in regard to impact. Specific designs of bolt-to-barrel lockup in MGs would present different issues if a weld has been done between the bolt lock and the breech, but this situation would be very unique to only a few types of MGs.
Even with poor quality welding, some welded MG receivers I have encountered, with several receiver sections welded back together have had held together perfectly well over many thousands of rounds fired.
MGs don't "blow up" due to welded receivers. They blow up due to detonations from bad ammo, out-of-battery ignitions and other reasons related to ammo or headspace, etc and not to welded receivers.
There is no need for hardening of any welded receiver, but evidence of brittleness in a seam should be addressed with annealing.
Internal joints of welded sections of receiver affecting rails and sliding surfaces should be finished and smoothed for smooth function of the action, but welding in itself won't affect wear of internals one way or another.
There are many thousands of MGs with welded receivers in the hands of shooters in the US and failures of the welds do happen, extremely rarely, and the damage can be repaired putting the gun back in operation.
FWIW

[sen24]

This really depends how on how it was cut and who welded it back up. I've seen mg34 receivers put together perfectly and some backyard jobs that were not safe. If the receiver is welded through correctly it will be structurally sound. If it's a torch cut receiver, cut far forward near the barrel you could have headspacing issues that are far more dangerous than structural integrity of the back half, which will simply lock up the action if the weld fails. But done right (and legally) these are as safe as the originals

[Leper]

There is no pressure containment in the main part of the receiver. It just acts as a guide for the bolt/carrier and a connecting point for the other points. If it is a badly done weld and cracks you will find a crack along the weld but not the weld itself. But you are likely not to notice until you clean your rifle.

[Blitzkrieg70]

MG 34 Receiver

Thanks for all the advice and input. I feel much better about having my receiver welded into semi automatic configuration. Who would you recommend to weld a MG 34 receiver and how much?