My Project

Ask your build questions here. Welding, assembly, etc.
robertmcw

Re: My Project

Post by robertmcw »

Richard, you state:

When I see the case-head from the exploded shell-case in the start of this thread.......I have to ask if this issue with your SA42 was corrected before moving on with the pierced primer/un-supported-primer issues (?). This case-explosion appears as an "un-locked" bolt-head or bolt-rollers un-locking early.......(IE: High-pressure still in the chamber as the bolt is unlocked from the barrel-extension). Condition of barrel-extension and bolt-rollers should have already been checked at this point prior to your first "range-outing" and a non-issue now.

After reading and re-reading you post and I was hit a duh moment – is possible that part of the problem is that if the length of the shroud is too short, could that mean that the rollers on the bolt head could fail to lock – even an few thousands in the length of the shroud?
I took this photo in this post years back and it says the total from the bump where the camming piece meets the bump to the bushing is 22.2”.

My shroud is 22 1/16 inches or 22.0625, not 22.2mm. Doing the math, that means my shroud is about .1375 inches short. If it that length is too short, is it possible then the rollers could not engage 100% with the barrel’s extension and then the camming piece could then not lock the rollers 100% as the barrel would be too long to fit and lock the rollers?

It that is happening is it possible that the brass is not engaging right (locking) with the rollers bolt head into the camming piece, right? If that would the case then it looks I need to cut the nose piece again and re-weld it.

If I need to re-weld it, should be just longer, like the 22.2mm say PLUS the width of a dime?

RM
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MG42frontendmeasurements[1].jpg
Blanksguy
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Re: My Project

Post by Blanksguy »

RM,
I see what you are saying.....but I believe that most builds will have enough room as the Barrel-Bearing is allowed/has room to move slightly forward. If it does not have enough room/length would it not show up as a barrel locking-piece not shouldered against the barrel-stop under the rear sight (?).

"Early-unlocking"/Timing of the unlocking of the bolt-rollers is what I believe that you are referring to (?).
This (if slightly early due to welding up a cut-receiver) should/could be adjustable by the relieving of the unlocking-projection at the front/inside of the rails. An accurate measurement of where this projection sits on an un-cut FA MG42 may assist you.......and measured from the rear of the barrel-stop inder the receiver to the start/front of the projections on the inside of the rails may help you in correcting this.......at which point, a new set of RTG-Parts rails (without rivet-holes) would allow you to set the rails to the corrected location and/or allow for modification of the starting-point of the forward/inner projection on the rails used to unlock the bolt-rollers (?).

Regards, RichardS
US Army, Retired
robertmcw

Re: My Project

Post by robertmcw »

I think you are going to but the camming piece is fixed and to adjust the rails would it not require to relocate the camming piece too?
The bolt head and the semi carrier slide all the way from the end to the camming piece like glass with no drag at all.
And the yes the camming piece is a WWII German matched set with no chips rust or dents and I would rate it a 95% set.
I do plan to rebuild the recuperator and I hope to find Bob Ness (if he is there) to rebuild it next week at Knob Creek.
RM
Blanksguy
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Re: My Project

Post by Blanksguy »

Yes (wasn't fully awake and Board doesn't allow me to change anything in posts later........), you are correct.....not the rails.....the Cam-Piece/"Trunnion" would either have to be relocated ..... or if possible, the barrel-stop would need to be moved slightly forward.....if they were out-of-spec. locations due to welding, .....and would require to check the barrel-bearing-keys vs. the "key-ways" in the receiver for interferences.

While talking about cam-piece-cutouts...........almost all builds using cut-receivers usually use the front of the cut-out location as the locating-point for their welding and adjusting for can-piece/"Trunnion" fitment........at that point, the bolt would unlock at the correct time............unless the cam-piece/"Trunnion" was either mismatched-halves, worn, or possibly made incorrectly. Timing should be based on the distance between the rear of the rear of the Barrel-Stop located under the rear-sight to the forward-edge of the cam-piece/"Trunnion" cutout in the receiver. Then, only the rear of the cam-piece/"Trunnion" cutout in the receiver would be adjusted to receive the cam-piece/"Trunnion" halves......which are originally serial-numbered "sets" and should match.

On the original posters challenges with his build, other items were brought up to be checked.......and without going back into the "Thread" it is un-known to me if they were cover (IE: The typing in my reply would go away if I go to look.).

Thanks again for catching my error (wasn't awake at moment of typing).
Regards, RichardS
US Army, Retired.
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