Problem with new AR build.

[Thrillz]

Its a pisol, but since its an AR15 build, I figure its more in tune with the rifle forum.

I pieced together a new 8" AR pistol and just finally had the chance to take it to the range. I only put about 10 rounds through it, since something felt off about it, and I didnt wanna press my luck, (never checked the headspace, thats a different story).

During those 10 or so rounds, the majority of the time, I was getting a failure to feed the next round. Seemed to extract and eject fine, but kept jamming up trying to push in a new round.

What it looks like to me (not a ton of experience with ARs or rifles in general) is that the bolt starts stripping off the round, then at some point in the cycle (maybe going up the feed ramps?) the bottom of the case dips below the bolt, which slams on the cartridge leaving the projectile side jammed up in the chamber/chamber lugs and the rear of the case jammed between the bottom of the bolt and the top of the mag.

I tried with a couple ammo brands I had, and tried with a Pmag and a Hexmag, and kept having the same problem.

I also noticed, on the face of the bolt, theres a brass colored ring after just those few shots, is that normal, or is it something I should watch/look out for? Not sure if thats related.

[Daycrawler]

Well first thing first get your head space checked and then get back to us. If your gun is unsafe, you are pushing your luck. The gun should be 100% before you fire it.

[DavidH]

Has nothing to do with Headspace. I*m sure your Headspace is fine. Also the brass color ring on the bolt face IS just that...Brass. Also not a problem. It*s from the pressure of the round being pushed back and the surface of the bolt face picking up particles of the brass.

Your issue can be a host of things. How is it jamming? Is it most of the way into battery? Or jamming just as the round is stripped from the mag? Does it happen at all if you charge a round? Does it look like it*s jamming into the feed ramps?

Are you using an M4 upper with M4 feed ramps on the barrel extension, or A3 upper with A3 feed ramps on the barrel extension? Mismatching them will cause jamming.

Should look like either of the top photos. Not the bottom.

[Xringshooter]

Sounds like it is short stroking (bolt not going back far enough to correctly strip and feed the next round). Could be caused by too heavy a buffer or buffer spring or it's not getting enough gas back through the gas port (blockage or too small a port). If it chambers a round when you initially pull the charging handle back completely then it probably is short stroking. Since it's a AR pistol, what weight buffer are you using and what type of buffer spring are you using?

[Thrillz]

Sounds like it is short stroking (bolt not going back far enough to correctly strip and feed the next round). Could be caused by too heavy a buffer or buffer spring or it's not getting enough gas back through the gas port (blockage or too small a port). If it chambers a round when you initially pull the charging handle back completely then it probably is short stroking. Since it's a AR pistol, what weight buffer are you using and what type of buffer spring are you using?

Not sure the buffer weight, but its the buffer tube/spring/buffer that came with the KAK Shockwave 2.0, so I assumed the set was put together for a pistol length gas system. When I put together the gas block/tube, I made sure to check that it was clear.

The round chambers and the bolt closes when I manually cycle it.

Has nothing to do with Headspace. I*m sure your Headspace is fine. Also the brass color ring on the bolt face IS just that...Brass. Also not a problem. It*s from the pressure of the round being pushed back and the surface of the bolt face picking up particles of the brass.

Your issue can be a host of things. How is it jamming? Is it most of the way into battery? Or jamming just as the round is stripped from the mag? Does it happen at all if you charge a round? Does it look like it*s jamming into the feed ramps?

Are you using an M4 upper with M4 feed ramps on the barrel extension, or A3 upper with A3 feed ramps on the barrel extension? Mismatching them will cause jamming.

Should look like either of the top photos. Not the bottom.

Ill have to double check when I get home to make sure (tbh I didnt even think of the feed ramps when I built the thing), but Im fairly sure it doesnt have mis matched ramps.

The way it jams, it LOOKS like the round gets stripped off just from the way it looks when I see the jam. The bolt makes it about half way forward before being stopped (or I should say the front of the carrier is about halfway in the ejection port window), with the back of the round under the bottom of the bolt (just about 1/8-1/4") and the front of the round jammed up in the chamber/bolt lugs. And if I remember right, the cartridge made it out of the magazine completely.

[DavidH]

Short stroking is a long shot...but easy to check. Load 1 round and fire. If the bolt locks back on empty magazine, it*s not short stroking.

[Gunplummer]

What caliber is it? It sounds like what 1911 .45 shooters call a "stovepipe". This is caused by the angle of the feed ramp being off and the bullet is kicking up before it can enter the chamber.

[Thrillz]

What caliber is it? It sounds like what 1911 .45 shooters call a "stovepipe". This is caused by the angle of the feed ramp being off and the bullet is kicking up before it can enter the chamber.

Was shooting some .223. Tried with steel case and brass cased, was running into the same issue.

I really want to check the headspace before I take it out again and try to run it. Its running with a phosphate carrier and a 158 carpenter steel, MPI'd bolt and the upper/lower are cerakoted (inside and out). I know putting it together everything was fitting really tight from the coating. Theres absolutely zero slop between the upper and lower, I mean its rock steady, but the BCG and charging handle seem to move freely (though they are rubbing some of the coating off, and it mixes with the grease/lube).

I do notice, in regards to headspace, that when theres a round or snapcap in, theres just a bit of "resistance" when the bolt locks/unlocks, when you cycle it manually. I really wanted to find some of the spent brass from it when I went, but I couldnt manage to find one from the rifle.

[Emptymag]

The KAK Shockwave Blade kit can be had with any number of buffer weights or if buying from a vendor, possibly not even a KAK buffer at all.
Depends of where you bought it and if it is a true "all KAK brand" kit. (many vendors sell the kits with generic, non-dimpled buffer tubes for example)

[Thrillz]

The KAK Shockwave Blade kit can be had with any number of buffer weights or if buying from a vendor, possibly not even a KAK buffer at all.
Depends of where you bought it and if it is a true "all KAK brand" kit. (many vendors sell the kits with generic, non-dimpled buffer tubes for example)

I bought the kit direct from KAKs website. If I remember correct, it comes with a carbine weight spring and buffer.

I checked the feed ramps as well, and the upper and barrel extension have matching ramps, so that shouldnt be an issue.