problem with AK build

[swift]

Ran into a problem with a RomyG build on an NDS3 receiver. The bolt carrier will close fine if the bolt is removed, but I can't get it to close with the bolt in the bolt carrier. It looks like the bolt won't rotate when it closes.

Any suggestions on what could be the problem? It's a matching parts kit.

[PolishMike]

Check the rail to trunnion mating. Make sure they are even and there is no difference in rail height and trunnion position. Try sliding just the bolt and see if it will close on the chamber. You may have to smooth out the trunnion or the guides on the bolt with a file.

[swift]

Mike,
The rail and trunion seem the same. When I did as you suggested, I found that the bolt does rotate slightly, but stops just before rotation in the trunion. It is touching the barrel and it seems that the groove in the trunnion is too small. I tried cleaning it with oil and a lot of green crud came out, but it still won't turn.

What I didn't mention was I lost the original barrel pin and I put another RomyG barrel pin in. It was a fine fit so I didn't think it was a problem.

[saki302]

Sounds like your headspace is off
When you pressed in the new pin it may have pushed your barrel back

-Dave

[PolishMike]

Mike,
The rail and trunion seem the same. When I did as you suggested, I found that the bolt does rotate slightly, but stops just before rotation in the trunion. It is touching the barrel and it seems that the groove in the trunnion is too small. I tried cleaning it with oil and a lot of green crud came out, but it still won't turn.

What I didn't mention was I lost the original barrel pin and I put another RomyG barrel pin in. It was a fine fit so I didn't think it was a problem.

I had to file down the guides on the bolt a little bit on my homebuilt receiver.

Also - check the ejector on the rail, make sure it doesn't extent too far. I had that happen on my rifle. The bolt would "bind" on the ejector.

[PolishMike]

Sounds like your headspace is off
When you pressed in the new pin it may have pushed your barrel back

-Dave

Doubt it has anything to do with headspace. The carrier is stopping before it reaches the front trunnion.

[ar15barrels]

Check the fit of the bolt in the trunion without the carrier.
Can you rotate it into lockup with your fingers?

If not, then the barrel is pressed too far into the trunion.

[ar15barrels]

Also - check the ejector on the rail, make sure it doesn't extent too far. I had that happen on my rifle. The bolt would "bind" on the ejector.

The guys at the AK build party tell me that it's normal to have to shorten the ejector until the bolt freely slides past it.
I had to take between 1/32" and 1/16" off mine to make it work properly.

[PolishMike]

The guys at the AK build party tell me that it's normal to have to shorten the ejector until the bolt freely slides past it.
I had to take between 1/32" and 1/16" off mine to make it work properly.

Its normal on a bent flat. I dont think you *should* have to on an NDS-3 but you never know.

I had that problem with a bent flat. didnt have to take too much off.

[weezil_boi]

Ive never heard of an NDS ejector needing to be filed down. Just flats.

[FEDUPWBS]

The guys at the AK build party tell me that it's normal to have to shorten the ejector until the bolt freely slides past it.
I had to take between 1/32" and 1/16" off mine to make it work properly.

Be very careful when you do this.

[ar15barrels]

Be very careful when you do this.

I did.
These hands have metalworking skills.

[swift]

Check the fit of the bolt in the trunion without the carrier.
Can you rotate it into lockup with your fingers?

If not, then the barrel is pressed too far into the trunion.

How can it be pressed too far into the trunnion if the barrel pin fits? If I push out the barrel 1/32" (or some small distance), won't I have a problem putting in the pin? I'm willing to try this before filing the receiver.

[ar15barrels]

How can it be pressed too far into the trunnion if the barrel pin fits? If I push out the barrel 1/32" (or some small distance), won't I have a problem putting in the pin? I'm willing to try this before filing the receiver.

The way it was explained to me was that the notch in the barrel is sometimes bigger than required.
You could press the barrel back out a little bit without removing the barrel pin.
You probably only need a few thousandths of an inch to make it work.

[motorhead]

check ejector first. should be <.560" from o/s of rec.. could be headspace issue although i've not heard of one tight enough to not close on empty chamber and still get bbl. pin back in. might have a burr or ding on locking lug or recess in trunnion.