Lets go back and start at the beginning with a couple questions......which the answers can help us help you.....
1: 8x57mm or 7.62x51mm/.308 (?).......and who manufactured the ammuntion that was used for this firing (?).
2: Booster-Cup/Nozzle hole-size (?).
3: Long or short Barrel-Bearing (?)......measurement in inches please:___________.
4: Original Receiver MG42, or something someone put together/welded together such as a "Post-86" gun (?).
We will also need a couple of clear photos of the gun from the right-side with parts removed and laid out next to gun so that we can see what you have to work with......to include the barrel/recoil-spring/bolt-assembly and buffer-unit......and flash-hider/booster-cup ("Nozzle) and barrel-bearing.
Also need to know if the bolt-head is from a practice-ammo/plastic-ammo set-up (?).........and see a clear photo of the bolt-head.
These may/may not be the only questions and/or requests for clear photos to be able to help you sort this out.
US Army, RET