Bolt will not fit

[makebang]

I am bout half done with a 4 cut weld up M53 build. Everything measures in spec from all the drawings i have found, camming piece fits perfectly, top cover fits perfectly, so far so good..... until i put the rails in and the bolt had to be hammered in to fit.
not good. A little filing, massaging here and there and now I can push it about half of the way forward before it stops and binds. The rails are just held in loosely with a couple temporary screws.

I am using new rails that seem to measure the same as the old ones except for being .010" wider so I filed them a bit to match.
Im kind of at a loss.... (and i have a lot of experience doing stuff like this, and a lot of gun builds under my belt)

Could I just have a slightly wider bolt? The receiver seems to measure but i cannot find all the measurements I want. (width, inside with of installed rails, bolt dimensions)
If I open the receiver any wider, my top cover isnt going to fit.
Any ideas?
Mu next option is to flatten out the rivet dimples just a bit but i really wanna know what's going on. The internals are not matching numbers to the receiver.

[JBaum]

The bolt is factory, so it is obviously within spec. The problem is how the rails fit in the receiver. Maybe some built up weld is holding the rails closer together. That's up to you to determine, as we can't see the receiver. It may require slightly flattening the receiver dimples.
Making the bolt fit an out of spec receiver isn't an option. Is there weld built up near the cam piece? That would hold the rails together toward the front. Make sure the rails aren't bowed/bent. If you're using bolts to hold the rails in, make sure they're tight and not in the way. It's better to flatten the rivet dimples a bit than grind on the rails.

[makebang]

Nah, there is no weld buildup. (i wish that was the issue lol!)
I won't go any more on the rails as now they match the original so no more should be needed. The caming piece fits perfect but the bolt won't even make it up that far.

The dimples on the receiver are very deep which is why i considered flattening them a touch. Im betting .020" or .030" on each side will get me where i need to be.

I don't know how much play those bolts normally have as i have never handled one before.

[Abominog]

If rails are .01 thicker each that’s .02 which can be a lot. Filing isn’t very accurate. Make sure they aren’t bowed too. A twist to the rewear will also cause binding.

Coat the bolt and carrier in dychem to see where the wear is.

The 42 is far more forgiving than the 34. That receiver takes hours of fitting and polishing.

[robertmcw]

Did you use a MG Rail Rivet Jig? You can spread the receiver with one. If you have one, measure the bolt and set the jig to the width of the bolt and see it the jig slips the track from the end to the camming piece. If you don’t have one, RTG has them pretty cheap.

[DARIVS ARCHITECTVS]

Paint some Prussian Blue on the bolt contact surfaces and see where the contact points are. A narrowing of the gap between the rails, or a twist in the rails could cause serious binding. It is important that the rails be straight or the bolt will not move smoothly, causing all sorts of feeding problems.Be PRECISE.

[42rocker]

Wish I could say that I've not seen this before. But here are my thoughts if this was a 4 cut then a lot of stuff is correct, that's good news. What does happen a lot is in the cutting up of the receiver the back area closes just enough to cause this problem. Stop forcing the bolt in. Measure the slot that the top of the bolt runs in. In several areas then check against the drawings on this site. You should find that slot closed to much. Open slot up causing the receiver to open which should allow the bolt to move better.
Also look for the rivet backups that you will use to set your rivets, make a pair or more. You can also use them to open up the receiver.

Good Luck

Later 42rocker

[Bil]

I don't know if it applies to your situation, but there is a right and left rail, one is thi
cker -or the other thinner-that can cause problems. ...bil

[makebang]

No, it was just a little tight i think from all the work and welding. A little massaging the receiver got it running smooth. now, after a few range trips it's super loose lol!

The receiver had a few small spots that were very slightly distorted. A little old school bodyshop sorcery (body man by trade) and it shot and ran fine first trip to the range.

[42rocker]

Big Fricking Hammer! Works every time. It seems that lots of times the receiver just somehow somewhere closes just a little bit to much for the bolt to move smoothly.
Glad you where able to get it going and had a good range test. Post a few pics some time. We love a little gun porn.
Good Luck with it.

Later 42rocker

[makebang]

I have a video up somewhere on the board showing the first test fire....

I'll throw up some more pics soon. It just needs a little more fire control work and then its all cosmetics.

Though im going to re rivet the rails next year. Ive done thousands of factory perfect AK rivets but I could not get these o come out nice no matter what sorcery i used.

[Abominog]

Note to restorers: when torch cut it is very common for receivers to warp. Also to be “sprung” meaning taking a shape due to metal memory. Make sure your bolt slides through each cut section BEFORE you reweld.

Then of course you can also have warp during the reweld too. But start and check even before you reweld. It’s more work, but keep the rails in place and deslag them too. Verify bolt slides freely. Then you can reweld or remove rails and reweld, your choice. And do the same for the cocking handle.