AR-15 cycling issues

[mookiie]

I recently built an Ar-15, with a rifle length gas system, fix luthr stock, and full rifle buffer system. My issue is the action seems to be short stroking, firing and ejecting the first round, however, the bolt fails to return far enough to the rear to feed the next round. I have tried adjusting the buffer weight as well as swapping in a carbine buffer. None of those options have worked does anyone have any suggestions? It is using a 20 or 22 in barrel chambered in .223 Wylde. Any help would be appreciated.

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[Sean357]

I only recently built one so not much experience, but is the gas block and tube perfectly aligned on the gas port? If it's partially blocked or misaligned it can affected bolt travel. Or is the gas block leaking? I've read of block and tube assemblies that don't have a great fit and leak too much and affect bolt travel also.

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[country gent]

Also check length alighnment on the gas block in the key. Gas rings in the bolt may be a small issue also. Alighnment of the block to gas port and tube to gas block is also important. Also check hole sizes of the gas port block and tube. block should be slightly bigger than the port and tube a little bigger than the block. if they are smaller or same size and miss alighned its a restriction. Ive seen issue where the port is in a land and not in the groove also. These barrels are timed in Gas port thru groove at length. barrel extension tight and pinned in to the port. Extension keyed to receiver. Gas block alighned to barrels port, and tube lighned to key and free thru the nut and receiver.

[JayT]

Check all your alignments and seatings in the gas system first. It may just be that simple. If all is good there, check the gas port itself for any obstructions, as well as the gas block. I would not go so far as to enlarging the gas port in the barrel, as it is a slippery slope to go down, because things can go sideways real quick if you don’t know exactly what you’re doing.

Without me knowing a whole lot about your internals, you may want to just break down and buy an adjustable gas block. The rifle length gas system is a little more difficult to tune (especially for subsonic), and I’ve always went right to an adjustable block when I do rifle builds, because even if you don’t own a suppressor, you may one day. If you buy an adjustable block, tune it slowly, as you don’t want to over gas the gun. Also, if you have a full-auto BCG, know that it as more weight than a semi-auto one, and more reciprocating mass takes more gas to cycle.

If you need any more help, feel free to PM me if you’d like.

[Joby]

The gas path issues seem to be covered sofar. Did you try different ammunition and another magazine. They are some other Common issues as well. And look at your brass for indications of a possible chamber issue.

[Moleman-]

Make sure to use a rifle buffer in a rifle buffer tube, and a carbine buffer in a carbine buffer tube. If you use a carbine buffer in a rifle buffer tube the bolt carrier can come back far enough for the gas key to strike the buffer tube tower and damage your lower receiver and buffer tube. If you've already checked that the gas ring gaps aren't lined up and made sure the bolt carrier was wet,checked for gas leaks, check the gas key for drag by seeing if the carrier alone will close completely by lowering it slowly (unloaded muzzle down no bolt) onto the gas tube. If it hangs up adjust (you know bend) the gas tube until it doesn't cause much drag on the gas key. The gas key hanging on the gas tube also points to the gas block being misaligned. Take the gas tube and block off. The passage in the gas block is generally 1/8". Look to see if the gas tube hole lines up well with the passage in the gas block. If not (and I've had it happen more than once) just kiss it with the largest size drill bit that will fit in the gas block passage. You're not removing much metal so go slow as the bit will want to grab. Also look at the carbon marks on the gas block and barrel journals to see if they were aligned well or not. Easy trick to set depth is to flip the gas block upside down (no tube installed) and center the gas port on the hole on the bottom of the gas block from where they drilled the passage. Measure the gap between the block and the step in the barrel with a feeler gauge. After doing all of that test it with decent quality factory ammo.

[WJP]

What ammo were you running? Barrel specifics would be nice to know as well. Manufacturers have a wide variety of gas port sizes. I've seen them all over the board. Pull the gas block, you'll be able to see a carbon ring on the barrel from where the block was lined up. If that's good then measure the gas port size.

[egg250]

Everyone's first reaction, misaligned gas block, is the obvious first choice. Did you use standard hand guard or some sort of free floated handguard? The gas port is located to allow for the thickness of the handguard plate retainer thingy that fits behind the gas block. If you don't use it, the result is normally a short stroking rifle. Assuming everything else checks out and you are using a free floated hand guard set up, get a 1/4" chamfer tool. Remove the gas block and chamfer the gas port. Look for signs of carbon in front of the gas port as this would confirm the misaligned gas block. This makes the opening of the port larger while maintaining the actual port size and allows for a slight misalignment of the gas block.

[blikseme300]

Everyone's first reaction, misaligned gas block, is the obvious first choice. Did you use standard hand guard or some sort of free floated handguard? The gas port is located to allow for the thickness of the handguard plate retainer thingy that fits behind the gas block. If you don't use it, the result is normally a short stroking rifle. Assuming everything else checks out and you are using a free floated hand guard set up, get a 1/4" chamfer tool. Remove the gas block and chamfer the gas port. Look for signs of carbon in front of the gas port as this would confirm the misaligned gas block. This makes the opening of the port larger while maintaining the actual port size and allows for a slight misalignment of the gas block.

I experienced this exact same thing a few years ago. What threw me was that the upper was bought as a complete unit from a reputable source.