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.

[sneaky one]

terry, triple check all the parts. I had a lower sent back to me from cav. arms-in 08' w/ a 9mm spring & buffer inside---I sent it empty. What fun that was to figure out.

H2-& a stock spring works well for most here-some use h3 & ??? spring. Keep it simple, that way you can always find a part -where ever you may roam.
Could it be--under loaded fact. ammo? That's what I see as a load is worked upward, that and the gas issue=too little to lock it back.

[terrywick4]

Not sure what it is, tried a new buffer spring and standard buffer
(been using H2) today and didn't help. Don't think it is a gas issue, I've run the gas block full open. I've hooked a air line to the gas tube and seems to have plenty when I blow thru it, more so than the 223. gonna have to wait till it warms up now, another snow storm is here and I'm hobbling around on a fractured leg.

[Shivesy]

In my opinion you accomplished nothing by adding a adjustable gas block and running it wide open. Would that not be the same as just a basic gas block? Adjustable gas block wide open and a basic gas block is going to flow the same amount of gas, whatever the gas port will allow. How far are your spent cartridges landing? I would quess 3'-4' would be common. Are they flying that far? I understand using a adjustable gas block if your over gassed because then you can tone down you gas flow. Some folks I have talked to open up their gas port a little larger than needed then tone it down as needed via an adjustable gas block. I don't really agree with that method but that is a different way to monitor gas flow.
As far as the dented cases. I was under the impression that it was a common issue. I run the soft piece of velcro on the deflector and now no more dented cases. Do you know your gas port size? Just a thought but you might want to open up your port hole just a tad more and if that don't do it then tone your gas back down with the adj. block. I also helped a friend with a situation like yours that was not gas related. The vendor sold him a longer buffer spring than what he needed. He had a collapsable stock and they sold him a fixed butt stock spring. We cut the spring down as a quick fix and his rifle cycled properly. Good luck and I hope you get it figured out.

[babaganoush]

As far as the dented cases. I was under the impression that it was a common issue. I run the soft piece of velcro on the deflector and now no more dented cases.

+1 on the gas block running WFO being counter productive.

I also had an issue with dented cases, and read about the velcro trick. Instead, I opted to shorten the ejector spring by 1.5 coils with a Dremel tool. It tamed that problem quite effectively. Brass now lands at my 4 o'clock at about 4 feet, with no dents and no brass transfer on the deflector.

[rushmc]

I had an issue with a lower and catch combination. (Brands dont matter at this point) What I had happening was the lower and catch lined up in such a way that the catch was hitting on the lower so it would not engage far enough to catch the bolt. I removed the catch, (I could see where it was hitting at that time, I found it by comparing how far it moved to a rifle that worked) filed off a bit of metal and it has worked ever since