AR-10 Bolt Travel

[gpr]

When an AR-10 cycles, does the BCG travel back until it bottoms out the buffer?

Reason I ask is i can't figure out a weird issue. The charging handle is coming unlatched when fired. thus on the last round of the mag the bolt locks back and the charging handle is loose and can slide back. It is really odd and annoying. I have installed a different billet ambidextrous charging handle and it is doing the same thing. I was originally thinking it was caused from recoil and the charging handle latch spring was too week and coming loose, now that a second one is doing this i'm thinking something else has to cause it.

My theory is that possibly the bolt is traveling too far back and the gas tube on top of the bcg is hitting the charging handle jarring it loose? is this a possibility? I don't know how else a charging handle latch could become dislodged???

I have been fighting issue after issue with this stag ar-10 since i got it. this is the last thing if i could figure out I think i would have a fairly solid gun finally....

 

[leftyk82]

Have you checked the following:

- burr or debris on the gas key
- burr or debris on the charging handle gas key relief
- alignment of the gas tube, gas key and charging handle (the bolt carrier sans bolt, should not bind on the gas tube when placed in the upper without the charging handle)

I'm just trying to think of things that would move the charging handle rearward upon firing.

 

[gpr]

Is the "gas key" the tube bolted to the top of the bolt carrier, which the gas tube slides into? Where would a bur be, on the outside? i guess i haven't check but never noticed anything. I'm suspecting maybe this gas key is hitting the back of the charging handle when the bolt is in the rear position.

This has happened now with two different charging handles, so i don't think the charging handle is the culprit.

I have had two different barrels on this gun and shimmed the barrel nut so i had perfect alignment of the gas tube. However, i don't see how a gas tube would knock loose the charging handle since it is stationary. But yes it is aligned and does not bind in the bcg or charging handle.


BTW, this has happened with the stock buffer, then I installed a tubbs flatwire. I also just installed the JP SCS heavy buffer. I did have to use the extra shim to make sure the SCS is in contact with the bolt carrier.

 

[Vio515]

Check the upper receiver where the charging handle latches. I suspect there isnt enough metal for it to grab there.

Have you shot this rifle a lot? Maybe that latch area has worn down?

My service rifle charging handle comes unlatched from time to time. It has many thousands of latch/unlatch cycles with CMP shooting and training. That same spot is slightly worn.

 

[gpr]

I have checked. while there are wear marks (which I think is mostly the finish worn off), if the charging handle is latched and i pull on it. It will not come unlatch. So either something is hitting it to make it unlatch, or the recoil impulse is causing it to jar free.

I haven't shot this rifle much as the barrel that came on it had a bad chamber. I'd guess maybe 200 rounds on it.

 

[Lawless]

With the rifle assembled and with enough light to see well into the ejection port, pull the charging handle fully rearward.

You should see only 1/10-1/8” clearance between the bolt face and bolt stop.

Big ARs regularly need to be shimmed to achieve proper bolt travel.

This can be done with washers or even quarters (with holes drilled for venting) but you can purchase buffer shims as well. They are placed in the bottom of the receiver extension to shorten travel.

9mm ARs have this issue regularly as well.

 

[gpr]

What does extra gap cause issues with? I did check mine and it was bigger then 1/8" so i put a thick washer behind the JP SCS, and this closed the distance down. It still jars the charging handle free when fired. I'm sure this isn't a big deal just never have seen it before, and really don't want the latch wearing out the receiver.

Plus for some reason it just bothers me and i have a hard time concentrating on shooting when i feel like a charging handle is gonna hit me in the lip....

I checked and there is no way the bolt gas key could go back far enough to jar the handle open. I am wondering if its simply from the recoil? I tried turning the gas block down, not sure what brand it is but it isn't shutting the gas off and still cycles with the screw all the way in. It also is kicking the cases out in the 4 o'clock position, so i don't think it is over gassed.

 

[Lawless]

What it’ll eventually do is break the bolt catch If it has too much clearance.

 

[Yondering]

What does extra gap cause issues with? I did check mine and it was bigger then 1/8" so i put a thick washer behind the JP SCS, and this closed the distance down. It still jars the charging handle free when fired. I'm sure this isn't a big deal just never have seen it before, and really don't want the latch wearing out the receiver.

Plus for some reason it just bothers me and i have a hard time concentrating on shooting when i feel like a charging handle is gonna hit me in the lip....

I checked and there is no way the bolt gas key could go back far enough to jar the handle open. I am wondering if its simply from the recoil? I tried turning the gas block down, not sure what brand it is but it isn't shutting the gas off and still cycles with the screw all the way in. It also is kicking the cases out in the 4 o'clock position, so i don't think it is over gassed.

Extra gap means the bolt carrier moves too far to the rear, which can be a big deal and eventually result in catastrophic failure. Shim it as described; a few quarters to figure out the thickness is an easy solution.