AR-15 short stroking?

[Zombie]

Hey guys, I've got a 14.5" carbine length AR here that is acting a little weird. When shooting factory PMC 55 gr or Winchester 45 gr frangible I think its short stroking, the round ejects but the next round gets jammed sideways when attempting to feed (I think the bolt carrier isn't going far enough backward). I confirmed this by loading a couple magazines with 1 round and firing, and it would not lock back. I then loaded some of my own reloaded 5.56 that are considerably hotter than factory .223 (but not maximum loads) and it locked back every time.

The weird thing is works fine for the first magazine full of PMC (so a clean rifle, or cold I guess). But then sometime after about 30 rounds it short strokes every shot. Any help? My full set up is:

14.5" spikes upper with carbine length gas system
Spikes BCG (full auto version)
Carbine buffer and spring

Thanks for any help!

 

[Joe30705]

Make sure your gas block is tight and everything is lined up...I put a low profile gas block on my M&P 15 for a full length quad rail and after a few weeks had the same problem...I actually had to buy a better gas block that locked tighter and wouldn't come loose...Avoid the gas blocks that have set screws that screw against the barrel

 

[rOmiLaYu]

PMC is under powered so that checks....also, if your chamber is tightish, that further exacerbates the situation. If you're gas block is lined up and everything is G2G, I'd just avoid PMC.

 

[Robnotfromga]

What type of gas block, pinned like a a1 sight or a low pro? What barrel? What's the gas port size.

If all that checks out,Change the buffer to a h buffer. The heavier buffer will add some dwell time, allowing for chamber pressure to drop before extraction. You may have to go to a h1. Heavier buffers are very helpful.

 

[Zombie]

What type of gas block, pinned like a a1 sight or a low pro? What barrel? What's the gas port size.

If all that checks out,Change the buffer to a h buffer. The heavier buffer will add some dwell time, allowing for chamber pressure to drop before extraction. You may have to go to a h1. Heavier buffers are very helpful.

Its a stock A2 style front gas post on a spikes barrel (came from them put together). I'm not sure on the gas port size.

Thats interesting about the buffer weight, intuitively thinking I would say I would want a lighter buffer, but you may be right about the dwell time. I will try that out. Thanks.

 

[Robnotfromga]

Its a stock A2 style front gas post on a spikes barrel (came from them put together). I'm not sure on the gas port size.

Thats interesting about the buffer weight, intuitively thinking I would say I would want a lighter buffer, but you may be right about the dwell time. I will try that out. Thanks.

The port could be the problem, you can drive the pins and pop off the sight. Use a drill bit to measure the hole size then mic the drill bit. Crude, but will work.

If you have a heavier buffer laying around try it. Also check to make sure your buffer spring is for a carbine and not a rifle. I think its 40 coils(Google check the # of coils)

Every AR I own or owned get a h/h1 buffer. The slower cycling also kills recoil, making follow up shots easier. Some guys run the heaviest buffer that reliably works.

 

[armory]

Also check the gas rings. I bought a factory new rifle once that had mangled gas rings.

 

[mtdawg169]

Its a stock A2 style front gas post on a spikes barrel (came from them put together). I'm not sure on the gas port size.

Thats interesting about the buffer weight, intuitively thinking I would say I would want a lighter buffer, but you may be right about the dwell time. I will try that out. Thanks.

You're right about the buffer. Usually if it's short stroking, you will want to go lighter. If you are positive it isn't leaking gas at the gas key and the gas rings are in good shape, I would contact Spike's for a replacement barrel. It's fairly unusual for a carbine barrel to short stroke due to higher gas port pressure. Is the gun new? It may just need to be broken in with better ammo.

 

[Adams454]

Check the gas rings on the bolt. It sounds to me like they may be lined up with each other. The gaps have to be offset.

 

[devin25gun]

Might have to step up the gas port in barrel as u are using a full auto carrier that is heavier for a reduced rate of fire. Or a lighter buffer and spring setup. Similiar threads on ar15.com for short stroking also.