Need some help with ar15 upper....

[azngunslngr11]

Pics added. Thanks to everyone for your help!

Got a question for you experts. Having an issue with my FA. Getting short stroke issues. Running a 11.5" upper, with carbine length gas tube. Having issues with 55 grain .223.

-Failure to lock back after last round,
-Will pick up next round, but gets stuck when the bolt is half way home.
-Tried H3, H2, H1, and standard Carbine buffer.
- upper and bolt are well lubed.
-replaced gas block with new one, checked alignment
-gas rings on bolt are good/not worn.
-no leaks in gas key
-i've tried different size buffer springs. Even shortened one by 2 coils. But started to get bolt bounce and FTF.
-x193 works well for the most part, but not 100% reliable.
- have tried different mags.

Any suggestions? Thinking about swapping out the DI system to a piston conversion. Piston conversions work well with FA?

Thanks guys!

 

[Necrosis]

Did it ever work correctly? Makes me think the gas port is undersize or partially blocked (lead from a 22LR conversion or copper/fouling?).

 

[Plinker66]

I’m no expert but based on my past mistakes I’d triple check the gas block alignment. They vary.

 

[Moondog1]

I’m no expert but based on my past mistakes I’d triple check the gas block

Yeah, what are the specs on the gas port diameter? Anyway to verify? Do rounds cycle correctly when you manually cycle the action? Do you have a different bcg to swap in? Sorry I know you asked for experts, I am no expert.

 

[greg vess]

Could be a obstruction in the gas block or a small gas port. Some manufacturers will tell you certain ammo will not run in their barrels due to small gas port. It also sounds like your extractor is to tight if it will not chamber the next round. So trying taking out the o-ring. It doesn't need it. Some guns don't need them while others will not run without them. It's a gun to gun deal. The deal with the ammo is the pressure of the rounds is not great enough to cycle the system. Try a better ammo and if that doesn't do it then take it to a gunsmith and have the port enlarged. Then install an adj. gas block to regulate the pressure.

The o-ring deal is the extractor could be to tight no letting the extractor slip over the edge of the cartridge rim. It's an easy and quick fix that will take 5 minutes to test and will rule out that potential problem if there is one there. If it doesn't resolve the issue just put it back in. Just turn the bolt over and push out the pin. the extractor will fall right out. Remove the o-ring and install the extrator in reverse order of take down procedure.

 

[01coltcolt]

I had this same scenario with a friends gun. It ended up being the gas hole in the barrel was too small. New barrel and she rocked. Also use Magpul mags

 

[Wallace's]

Need to know more info.

Who made the barrel (and other components)?
How did you check gas block alignment? (95%+ this is the problem) -> is the barrel dimpled?
Verifying a gas key is sealing is very difficult unless it obviously loose.
What size gas port? No, calipers will not suffice. You need a pin gauge set. (knowing who made the barrel would help possibly without needing a gauge pin set)
What brand of XM193?
How did you verify the gas rings were ok?

Also, absolutely no need to cut a buffer spring. Waste of a spring.

Short stroking is almost always a lack of gas issue -> very rare instance of a too small gas port (most make their slut sized ports to cycle cheap ammo without complaints), gas port obstructed from a manufacturer possibly drilling the port after CL, gas block not drilled for a gas port (airsoft, and yes I have seen people use these), carrier key not drilled for a gas passage (yes, Anderson has let some of these slip out the door), leaking gas key (did you check the fasteners were tight?), gas tube installed upside down (yep, seen that one way too many times now), blown primer in carrier key (yes, it literally can happen), incorrectly manufactured buffer spring, severely worn gas rings, gas tube installed in front of the roll pin (yes, I know, but people can screw up a bowling ball in a sandbox), carrier expansion chamber too tight from improper machining or CL and the bolt binds inside the carrier, Gas tube worn and the flared bell no longer seals in the gas key, gas vents in carrier missing (Radical with their finest QC controls), etc...

 

[madmarinehays]

I had this same scenario with a friends gun. It ended up being the gas hole in the barrel was too small. New barrel and she rocked. Also use Magpul mags

OP - This

Sound like the gas hole is to small, not enough gas pressure.

 

[azngunslngr11]

Hey Guys, thanks for all the responses! Here's what I've done:

-Cleaned gas port and checked Gas block alignment
-checked port for obstructions
-swapped out buffer spring for a lighter spring, and used a carbine weighted buffer.
----got the same results.


-Swapped to x193 ammo, and started to function normally. But got FTF with primer strikes. (Think this is due to bolt bounce with lack of buffer weight and buffer spring tension.)
-swapped out buffer spring for regular spring, and went to H1 buffer. No issues with x193 ammo.
-loaded up .223 PMC Bronze, started short stroke issues again.

-Swapped gas block out for a new gas block, re- cleaned gas tube, gas port and checked alignment
-.223 PMC bronze still short stroking.

If i decide to drill out the gas port, how much should I do? (I'm not married to the barrel/upper i'm running. I got a dedicated upper in order not to put wear and tear on the original Colt upper and Barrel). From other threads I've read, could there be any issues with the lack of Dwell time between the bullet passing the gas port and exiting the muzzle? The barrel is a 5.56 nato barrel with a 1:7 twist, with a carbine length gas system. So the total bullet travel between the gas port and the muzzle is about 2 inches, which may not have enough pressure to build up behind the lower powered .223?

Thanks again Guys!

 

[azngunslngr11]

Sorry, here are some answers to other questions:

Upper is made by X-Products
Barrel is made by Faxon Firearms
Gas block made by Midwest Industries
Gas tube- Un-known maker
Nickel boron Bolt/BCG- Made by Areo Precision.