Need help- AR-15 is now single shot

[556BlackRifle]

I agree with the others that there is most likely something going on with the gas system. The low profile front sight block you mentioned wouldn't be made of aluminum would it? If so it could've eroded and the gas is leaking out. If not that could be a misaligned block, poor seal at the point where the gas tube enters the gas block, gas tube not mating with the carrier key, loose carrier key, leaking / split tube, or gas rings.

Pull the BCG and check the carrier key for tightness and inspect the end of the gas tube that mates with the carrier. If that looks okay check your gas rings. If they look okay remove the handguard and inspect the entire gas system using a good light source and if need be a magnifying glass. If it's leaking you should see evidence in the form of carbon fouling. Depending how many rounds you fired, it may be minimal so looking closely with good light and magnification is essential. (Especially if you have old eyes like I do. )

Good luck and please let us know what you've found.

[cutter_spc]

No such thing as coincidences. If you rotate the tires on your car and the next trip you take down the road one of the wheels fall off.........well you probably did something wrong in the wheel area! Regardless what the smith says, take hard look at the gas block and tube, it's the only thing you said you messed with. Clamp on blocks are notorious for coming loose, I would bet it either slid up or rotated and carbon now has it wedged to make you think it's tight. How much wiggle room does the end cap in front of the hand guard have now?

You could just take the gas block off to confirm, not hard to do, and not hard to put back on.

[WBAR]

Thanks, guys, for your thoughtful responses. There does appear to be some carbon (blackness) on the gas tube near where it goes into the gas block. The end cap which used to have a fair amount of wiggle with the GI guards now has little to none. It's quite possible that the gas block is aluminum. Bill

[Dukr]

Some carbon deposits are normal.

DK

[BooneGA]

Check the gas key. If not properly staked it will come lose and your rifle will go single shot. I had an old bushmaster do this and fixed it with a flathead screwdriver and hammer.

Rick

[fpharryc]

I always just remove the lower, remove the BCG/CH, hold and blow the barrel in my mouth, then feel with pinkie to see if there is any airflow through gas tube in the chamber, for a quick initial diagnosis.

I know. But it's mine anyway, either gun or saliva.

[_Stormin_]

I always just remove the lower, remove the BCG/CH, hold and blow the barrel in my mouth, then feel with pinkie to see if there is any airflow through gas tube in the chamber, for a quick initial diagnosis.

OK, this is just Shake Weight funny...

[Ryno12]

I always just remove the lower, remove the BCG/CH, hold and blow the barrel in my mouth, then feel with pinkie to see if there is any airflow through gas tube in the chamber, for a quick initial diagnosis.

I know. But it's mine anyway, either gun or saliva.

You "always"?? How often do you need to do that? Maybe you need a better AR.

[26 Inf]

Have you cleaned the BCG within the time frame of the hand guard swap? If so there any chance you lost a Q-tip end in the gas key when you were cleaning it?

The gas passages drilled into the gas block are quite a bit larger than the port in the barrel. I'd think that if it had twisted enough to reduce flow so the weapon doesn't even try to cycle, you'd see it.

The MOE Handguards on my daughters' were a snug fit, but not sure if that is really relevant, theirs has a pinned A2 front sight base, only attesting that the MOE's seemed to fit snugger than the originals.

[Iraqgunz]

This make little sense without pics. Changing a handguard does not cause this. I suspect you have some with a Picatinny type gas block. It probably became misaligned. Also, a proper gas block is not made from aluminum.