AR being uncooperative

[Perplexed]

With the goal of building an AR in 5.56 that had a very mild recoil, I put together one with an 18" barrel with a Wylde chamber, rifle-length gas, and a 1:7 twist. I can't recall who made the barrel, though. I installed a Precision Armaments M4-72 compensator, and used an Aero Precision upper with a WMD NiB bcg, Velocity drop-in trigger with 4 lb pull, and a standard buffer (~2.8 ounces) and spring in a M4 style collapsible stock.

I ended up with an AR that indeed had very little recoil, but I ran into a problem. Once in a while the rifle would fire and cycle properly, but about 8 or 9 times out of 10 it would eject the spent round and fail to chamber a new round. I tried Wolf Gold 55-grain .223 FMJ and Champion 62-grain 5.56 FMJ, with several MagPul P-Mag's and 10- and 20-round metal USGI mags. I know the AR is probably short-stroking, which is why I tried a standard buffer and spring, but to no avail. I checked the gas block for proper alignment with the gas port, and it looked good - very little soot evident around the latter. I even tried clipping one coil from the spring, but it made no difference, and after clipping a second coil, the spent Champion 5.56 round was stuck in the chamber and I had to mortar the AR to get it out. I stopped at that point.

How does one make sure the gas block and port are aligned properly? Am I looking at having to open the gas port? If so, what's the best way to go about this, or are there other remedies I can try without sacrificing the amount of recoil reduction the AR currently has? TIA.

 

[dlbleak]

Mmm, little soot around the gas opening could be tell-tale sign that it is not aligned. I had the same issue with one and just left the hand guard off at the range. With my allen or torx handy, I fiddled with it until it cycled right. By the time I was done, it looked like there was no way it could be straight. It cycled correctly and that's where I left it.
Good luck with it.

 

[bd79]

What kind of gas block do you have?

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[SPDguns]

Bear with me while I try to explain this--Make sure that the gas hole in the barrel is lined up with the hole in the gas block parallel to the bore axis (front to back). Some blocks don't take into account that the front handguard cap is missing, thus making the gas block too close to the upper receiver the distance of the thickness of the cap. The solution is to install a shim washer the thickeness of the missing cap to push the gas block forward into the correct position.

 

[Perplexed]

Thanks for the comments, folks. It's a generic low-profile gas block - I think I picked it up from FBT, but I can't be sure. I did wonder about the front/rear and side-to-side alignment of the block; I made darn sure it was aligned vertically, and I did tighten it down about the width of a playing card ahead of the stop on the barrel.

I guess I'll just have to do what dbleak did - try fiddling with the alignment of the gas block while at the range and see if that doesn't work. Btw, when I mentioned sooting, I meant no more than usual - the tiny ring around the edge of the gas port. Not a huge swath extending along the barrel.

Even with the rifle length gas and extreme compensator, and weak .223 ammo, one can still expect the AR to cycle with a properly aligned gas block? In other words, the main culprit would be a misalgned block?

 

[SMS]

Gas key on the carrier tight and properly pinned?

Magazine catch being too loose or too tight can also cause similar feed issues.

 

[FOG]

Gas key on the carrier tight and properly pinned?

.

I had the same problem and what SMS just mentioned was the culprit. Tightened it up and got it properly staked and haven't had a problem 1000+ rounds later.



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[lasher]

i have found, recentlly, several gas tubes that are semi blocked, for lack of a better term. i now use a piece of stripped 12 gauge copper romex and feed it in and out of the tubes several times. after install i put the nozzle of a hornady one shot can into the tube on the receiver side, turn muzzle down and spray, if i get one shot out the muzzle it's usually good to go. i've had to make several gas ports larger on shorter barrels because i'm using much faster powder, i use a #43 wire bit for that. 3/32nds would probably require an adjustable block. i run a dowel down the bore to stop the bit tip from biting the other side, put on drill press use moderately light downward pressure and basically let the bit pull it's way thru. also check to see if the tube port is obscured by the block, there have been tales of the tube port not aligning with the block port, i only use set screw blocks so it's easy to check after install into the block. be sure the gas rings on the bolt are staggered where none of the gaps line up.

 

[Ignored Member]

With the several AR's I've put together, I've mainly used a low pro gas block (usually a $20 YHM) and had it flush with the lip of the barrel. The only time I've found that the gas block doesn't go flush is when using the standard sight tower gas block.

Try using a light weight carrier too.

 

[Ignored Member]

Staggering the rings on the bolt don't make the slightest bit of difference.