bolt not locking back on last shot

[terrywick4]

I have an issue that I can't seem to get figured out. When I shoot my last shot my bolt doesn't lock back. I can pull the charging handle back on an empty mag and the bolt will lock back on it own, but when it is fired it doesn't? I Put a adjustable gas block on today thinking it might solve the problem. It did fix the dents in the brass but It still doesn't lock back. I tried the upper on a different stock lower (colt law enforcment)and still doesn't lock back. Any Ideas?

[babaganoush]

Here are some things that come to mind, in no particular order...

Have you tried other magazines?
Is the BCG traveling free, and unobstructed?
Have you tried lubing the BCG?
Do you have another BCG to try? (Emphasis on the bolt.)
Do the lowers use any Bolt Release add-ons (BAT Lever, etc.)?

With enough time/spare parts you should be able to isolate the issue.

[LRRPF52]

What load is it you are running?
What's your current buffer weight?
What weight/type Bolt Carrier do you have?
Is this on your 24" RLGS rig?

[terrywick4]

This is on my 24 " satern barrel Using factory Hornady 123 A-Max, Have tried, 3 different bolt carriers, two different bolts, 10 different mags (mix between 5,10 17 and 25 rounders), 3 different buffers (standard carbine buffer, H2 and H3), two different lowers (maybe a third) no add ons to the bolt release. Everyother operation of this guns runs flawless. Is wierd because with an empty magazine I can pull the bolt back and it will lock by itself.

[adayton]

Has it ever worked OK? or did it just start recently?

[LRRPF52]

So it looks like either too much gas too fast, or too little gas. Is your brass beat up badly, particularly extractor gouges on the rims? Any bulged case bases, where they look like a belted magnum?

If not, then your gas port might be too small, but with a 24" barrel/RLGS, you have a lot of dwell time, especially with the 123gr A-MAX. What is your gas block setting for these failure to lock scenarios? Did you record the gas port diameter of your barrel before installing the gas block by any chance?

[terrywick4]

So it looks like either too much gas too fast, or too little gas. Is your brass beat up badly, particularly extractor gouges on the rims? Any bulged case bases, where they look like a belted magnum?

If not, then your gas port might be too small, but with a 24" barrel/RLGS, you have a lot of dwell time, especially with the 123gr A-MAX. What is your gas block setting for these failure to lock scenarios? Did you record the gas port diameter of your barrel before installing the gas block by any chance?

I was thinking gas as well that is why I put an adjustable one on today, after a box of shells (hard to get shells) I have concluded that it's not gas issue. I say that because I went from not cycling to beating the crap out of the brass (big dents where it hits the deflector) and still no lock. I think this one did lock back before I sent the barrel to get coated, don't remember if it started when I went to the UBR stock (same time frame as coating barrel) or sometime else. The previous stock was a collapsible and I have it on a different lower that I tried also with no success.

[Drifter]

I think this one did lock back before I sent the barrel to get coated...

Was gas port area of the barrel coated, or was it masked off? Wondering if coating got into the port hole, effectively making it smaller.

[rushmc]

I have had this happen twice
1st time (I was really new to the black rifle) I got too much oil in the buffer tube. Acted something like an O ring and would not let the buffer slide. Cleaned the oil and it worked fine

2nd time was a flat wire heavy duty spring with an H3 buffer. Went to a more stock spring and that cured that problem

[babaganoush]

I had an issue with mine that, in addition to a FTF would often fail to lock on empty. While installing the barrel, I'd apparently overtightened the clamshell holder, and had somehow deformed the upper. It prevented any magazines from seating correctly and it, too, would always lock back when manually cycling the bolt. Mine didn't fail to lock on empty as consistently as Terry's, but it was one of those "drive you nuts" problems. There were definite marks on all the metal magazines where they were contacting the upper receiver, which is what finally lead me to check. Swapped the upper and made all the above issues go away.

[terrywick4]

I think I might have figured this out. I put in some "twang busters" (which I put in all my lowers) and I think this is allowing my buffer to bottom out too soon. When I pull the slide back manually the bolt just barely goes far enough to catch. I took the twang buster out and now have more than a 1/4 inch. Will have to wait and see if it fixes the problem.

[babaganoush]

I think you may have a winner, there. With little or no additional clearance, the buffer was/is likely rebounding before the follower can get into position. (Note to self - aftermarket gimmicks always profit those selling them.) I personally never let the "sproing" sound bother me. It's when the rifle doesn't make it that I know that a reload is imminent.

[Variable]

LOL!


OP- That wasn't aimed directly at you, but more towards the AR market in general of late. It started with accu-wedges, anti-rotation pins, etc., and it's turned into an entire storm of aftermarket stuff that is mostly supefluous fluff and doesn't actually do much or anything but make someone else money.

People bring me ARs all the time wanting to know why they don't work right, and 95% of the time it is one of two things:

1.) A franken-gun made from fly by night aftermarket parts... (With something turning out to be horribly out of spec)

2.) A normal functional piece modded with mud flaps, kick stands, curb feelers, and a sky hook.LOL! (Which then interfere with normal function)

I guess I shouldn't complain about what folks do with their own personal guns, they got a right to tinker with whatever they want.... I'm just crotchety in my old age.LOL

[pappy42]

I think I might have figured this out. I put in some "twang busters" (which I put in all my lowers) and I think this is allowing my buffer to bottom out too soon. When I pull the slide back manually the bolt just barely goes far enough to catch. I took the twang buster out and now have more than a 1/4 inch. Will have to wait and see if it fixes the problem.

Let us know if this works for you. Might save the next shooter.

[terrywick4]

Well that did't fix it..Guess I will live with it. I have no other issues with it, feed well, extracts well, just doesn't lock back when empty. Next time out with my brother I'll have to switch out lowers (was exactly same as mine before I switched out gas blocks to try and fix this issue) to see if his locks back in mine and visa versa.