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MG42 - Bolt Rail Instead of Rivets?


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You don't specific if the gun is semi or FA. For riveting the rails it is really necessary to have the right tools for the job which have to be custom made for the rivets to be set properly and the half round set heads to be correct in shape, etc on the outside.

It is important that the fit of the rivet or screw shank be tight through the mating holes because there is a fierce upward lift of the bolt as it recoils to the rear. This lift puts a hump in the top rail on FA guns after a while. Any looseness of the fit of the rivets or screws will allow the rail to move up and down which can affect function.

the bolt rails are slotted so there is some leeway in protrusion of the screw or rivet into the inside of the rail and not hit the bolt. But not much!
Screws loosen up unless welded on the inside of the rail to prevent rotation of the screws on FA guns. Locktite, etc will not do it, but maybe on a semi. At least you can reapply the Locktite. The vIbration harmonics on FA 42s is fierce and destructive and can loosen tight rivets eventually. Takes a lot of shooting though.

I've seen rails on post sample FA 42s that were plug welded through the rivet holes where the welds have broken. Plug welding the receiver and rail together through the holes needs care to insure that the weld actually goes through both holes fully to the other side to secure the rails.

Screws will work. FWIW

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Hoo boy! Now you're getting into really tricky territory. If there were a concave button head cutting cutting tool designed to round off cheese head screws to the shape and size of a rivet head, I would have worn out half a dozen by now. Shaping of the Allen head screws to mimic a rivet head after installation makes riveting look like the easy way.
If you are going down that path, my suggestion would be to do rounding of the Allen head screw first . The hex will be unaffected except at the top where it will be welded anyway. Then your sculpting only has to be done at the top of the screw and not at the intersection of the receiver and screw head.

I've done the following on a few PS 42s years ago.

Lightly chamfer the I INSIDE of each rivet hole in the rails. Select your button head rivets, not iron, but steel. Shank length 1/16" plus longer than thickness of rail and receiver wall pressed together, measured with rail assembled in place in receiver. This free end will be welded to flow back into the chamfer. I gas welded the rivet ends.
Using small fitted machine screws and nuts, bolt both rails into place from inside of rail at end holes leaving the middle ones open. I recall using 10/32 machine screws or whatever fits easily. Reduce bolt head ODs and thickness so they don't interfere with bolt travel on the inside of the rails. Check free bolt travel frequently!

Check the free movement of the bolt and adjust until it slides freely. This is critical!
True the open holes and get or slightly turn down rivets with shanks so they are a press fit into the trued hole. Cut to length noted above or grind them to proper length.

Add another small machine screw into the third hole so the open hole in between is clamped against the receiver

Insert rivet into open hole and clamp it with C clamp across receiver to press the base of the rivet head against the receiver.

Weld the free end of the rivet on the inside of the rail.

Check free travel of bolt.

Repeat with the other holes.

There's no way that I know of to create the rivet heads without a lot of work. FWIW


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As a former MG-42 owner, I would say no, screws are insufficient, particularly long term. The vibrations when firing are enormous, and screws will fatigue and break. Do it right. Use rivets and a proper press, the same as your would in an AK-47 receiver. With such an expensive gun, why go half way on quality?

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DARVIS.....relax. The poster is building a post-sample MG42. It is NOT a vintage transferable!!

Nothing wrong with using screws if the threading of the rail holes is through both rail and receiver, not just into the rails, and the screws are properly tack welded on the inside of the rail. Builders that use screws tend to just tap the rails and use Locktite which does not hold. But, they can just retighten the screws!

Having built many post-sample 42s and a handful of semi-autos, I've had conversations with many builders, some of whom have successfully used screws in FA post-samples. They were successful because the assembly was thoughtful and mechanically sound.

I have also assembled rails using rivets in repairs of transferable 42s along with many other simple and complex repairs of many of these MGs. FWIW

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I need to replace the rails in my post sample M53 too. What about this: use rivets, but instead of pressing them use a tig welder. Tig wash the rivet down to the receiver and when it cools it'll shrink and make it tight. This is the method I'm going to try. What do you think?

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