I've got a build that I got some time ago that's giving me fits.  Maybe you guys can help me figure out what's up with it.

I bought the rifle from another guy locally, and it did fine.  I decided to change out the handguard to a YHM one, with a low profile
YHM gas block.  As I remember (this started last year), it worked fine then too.  Until the middle of one range trip when it decided it was a bolt gun instead of an AR.
It suddenly stopped ejecting the spent cartridge and picking up a new one.  You can fire it one round at a time by cycling through with the charging handle,
but it won't function in SA.

I swapped out BCG's with another, known working carbine, and nothing changed. Same problem. So I guess I can count that out- extractor, etc.

Does this sound like a gas issue to you all?  The gas block is tight to the barrel, but I can't figure out what else might be causing the issue.

Appreciate your $.02.......

Thanks

Have you checked headspace on it? How does the fired brass look?

Sounds like gas issue to me, if it is stripping rounds manually. It may be short stroking?

Had this issue as well. My low profile gas block had walked forward about 1/4" and covered the gas hole, preventing the bolt from cycling. I used lock-tite and retightened and never had the issue again.

This is my first AR build I used. Everything here sounds exactly what issues I'm having with the addition to when I try to pull charging handle back it is very tight. Any suggestions? I didn't change anything as far as parts go just used the ones in the kit. I did lose or forgot the gas tube pin the first time and had to get a new carbine gas tube and gas block (this time ensuring the gas tube pin was in place) but that didn't fix it either. The problem is still there and now the tightness when cycling the charging handle. Have been using Federal 556 M193 Ammo I got from Cabela's

Spikes Lower
DPMS SOCOM Flat top upper (complete kit) (I know I should know the specs of the kit but not sure of all of them)
1:7 twist Carbine Chrom Moly barrel
Carbine gas tube
?? BCG
?? Trigger
Any suggestions or ideas on how to correct this would be very helpful.
If your gas block walks that much won't your hand guards get loose also? Mine are still tight and in place

Dano usually nails it but it won't hurt to do the following.

Try to confirm the gas is getting to the carrier.  Buy some windshield washer nozzle hose, slip it over the gas tube in the receiver and blow.  If you can hear/feel air blowing into your barrel you may be OK there.

Scrub the heck out of the chamber with CLP and a brush, and try it again.

Same situation.   I've built two AR-15 pistols.  One with 10.5" barrel and one with 11.5" barrel.   Took both to range this morning and neither would act like a semi-auto.   Both fired, fairly accurate at 50 yards but neither would eject fired round or chamber new round on consistent basis.   Both would do it occasionally, like once each ten cycles, but that is it.  Otherwise I had a short bolt gun.   If the "pistols" had not ejected and chambered at all, I could sort of understand it but both would cycle correctly once in a while.   No order to the cycling, just once in a while with no constant series.   Ideas or help, anyone, please?

From my first post. I tore down rifle and found that gas tube was incorrectly installed (my mistake again) but when I took it back to range (after fixing gas tube), now I can fire and it will eject one or two then I get a dead trigger pull (at least that's what the range guy called it). It acts like the safety has been switched. So I pull the charging handle eject that round shoot a couple more times then same thing. Could I still be having a gas tube problem, a buffer problem or what?

Any help would be greatly appreciated