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  1. #1
    Needs More Cowbell! Kyle's Avatar
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    Angry Short stroking AR-15... help!

    Ok... so my 20" rifle length AR-15 started short stroking after I replaced my gas block (I am 99% sure that is where my issue lies) however, the new gas block, from what I can tell, is sitting perfectly above the gas port; I have folding BUIS with my front sight attached to the new block and it is sitting 100% perfectly level and is dead on accurate according to the laser bore sight and range results. Could the gas port on the block be smaller than the original? is there something not right with my tube and how it is pinned? my gas key is not loose, nore is there any friction between it and the gas tube. The gas tube appears to be perfectly straight.

    *I swapped lowers with my friend and it cycled a bit better but still short stroked every few rounds (he has a bit lighter buffer spring and both of our buffers ar spikes ST-T2's)

    *I am using the same cheapo ammo I have always used, but it does cycle higher quality ammo no problem.

    Any help or suggestions would be GREAT!

  2. #2
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    Re: Short stroking AR-15... help!

    In the auto repair biz, if something goes wrong after a service, you look at what you did at the service because 99% of the time that's where the problem lies.

    Gas block is the problem, somehow. Either mounting position or the hole in the block (though the gas port is typically in the barrel, with the hole in the block larger), or the gas tube somehow got screwed up.
    Don't mind me, I'm just making sure I'm on all of the watch lists.

  3. #3
    Needs More Cowbell! Kyle's Avatar
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    Re: Short stroking AR-15... help!

    Quote Originally Posted by M. Sage View Post
    In the auto repair biz, if something goes wrong after a service, you look at what you did at the service because 99% of the time that's where the problem lies.

    Gas block is the problem, somehow. Either mounting position or the hole in the block (though the gas port is typically in the barrel, with the hole in the block larger), or the gas tube somehow got screwed up.
    That is what I have been thinking, I am relatively new to the AR world so I am just making sure I am on the right track!

  4. #4
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    Re: Short stroking AR-15... help!

    Tandke a drill bit by hand and use it to clean any burrs off the new block make sure there is nothing obstructing flow. Then remount it and test. Something is for sure blocking flow

  5. #5
    Senior Member ROGER4314's Avatar
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    Re: Short stroking AR-15... help!

    There is no guarantee that when the gas block was made, the hole in it was actually unobstructed or the correct size. Those parts aren't expensive. Try another one......OR ..... If you return to the original A2 front assembly and the rifle functions, the spotlight is on the gas block. Make only one change at a time then test fire.

    If the rifle fires better ammo perfectly, that may be your answer. During the ammo crunch, our club match director got Wolf .223 for our 200 yard matches. One of the shooters had an AR that would only single fire the Wolf and it had to be manually ejected. I fired Wolf, found it shot to the same point of aim as Win White Box and concluded they were operating at the same pressure. His rifle just wouldn't stand for firing Wolf ammo and it short stroked every time. Of my AR's, some will eat the cheap stuff like candy. Others will barf & jam with it. Who knows?

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  6. #6
    Needs More Cowbell! Kyle's Avatar
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    Re: Short stroking AR-15... help!

    Quote Originally Posted by chubbyzook View Post
    Tandke a drill bit by hand and use it to clean any burrs off the new block make sure there is nothing obstructing flow. Then remount it and test. Something is for sure blocking flow
    Ill give that a try!

  7. #7
    Needs More Cowbell! Kyle's Avatar
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    Re: Short stroking AR-15... help!

    Quote Originally Posted by ROGER4314 View Post
    There is no guarantee that when the gas block was made, the hole in it was actually unobstructed or the correct size. Those parts aren't expensive. Try another one......OR ..... If you return to the original A2 front assembly and the rifle functions, the spotlight is on the gas block. Make only one change at a time then test fire.

    If the rifle fires better ammo perfectly, that may be your answer. During the ammo crunch, our club match director got Wolf .223 for our 200 yard matches. One of the shooters had an AR that would only single fire the Wolf and it had to be manually ejected. I fired Wolf, found it shot to the same point of aim as Win White Box and concluded they were operating at the same pressure. His rifle just wouldn't stand for firing Wolf ammo and it short stroked every time. Of my AR's, some will eat the cheap stuff like candy. Others will barf & jam with it. Who knows?

    Flash
    My carbine that I just sold begged for more crap ammo. Before I changed the gas block it short stroked until I realized my gas tube was bent on the end and was grinding agains the gas key just enough to cause problems. I fixed it, and It shot crap ammo no problem but you could feel it wasnt throwing the bolt back very far. Now with the new gas block I eject the shell without issue but it will either completely pass up the next round or it will grab it just enough to jam it up. I have tried several different mags and it is the same issue. Could it be that the monarch ammo is just cheap and under powered enough to piss me off?

    Now I went to pull apart my gas block and the hole is for sure sitting over the barrels port as there was carbon in a perfect circle around the barrel port the same size as the hole in the gas block also indicating (correct me if I am wrong on any of this) that I have a proper seal with no leaks on the gas block.Could I possibly be leaking at the gas tube roll pin? I lost the one that came with the gas block like a damn idiot, so I used the one from my old front sight block. I plink a lot so I hate to think that I may have to buy more expensive ammo just to pop tin cans. Ill sell the damn thing or trade it if that is the case.

    rifle specs:

    Colt upper receiver with a 20" FN barrel, smith vortex flash hider, chrome BCG W/ no forward assist , spikes ST-T2 buffer and standard buffer spring.

  8. #8
    Eats breakfast everyday codygjohnson's Avatar
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    Re: Short stroking AR-15... help!

    Quote Originally Posted by Kyle View Post
    rifle specs:

    Colt upper receiver with a 20" FN barrel, smith vortex flash hider, chrome BCG W/ no forward assist , spikes ST-T2 buffer and standard buffer spring.
    I'm surprised you are running a 4.6oz buffer on a 20" barrel. I would have thought that was too heavy. When you say "standard spring" do you mean carbine or rifle? I'm almost positive you're running a carbine receiver extension and spring, but I thought I'd find out for sure.

    I would say, from what I've read here, that your new gas block is more restrictive than the old one. You are running the heaviest carbine buffer available, so it's pretty likely that's the culprit. I would suggest you move back to a H1 (3.7oz) or a carbine (3oz) buffer.
    Quote Originally Posted by Wolfwood View Post
    i'm just an idiot asshat jerk off and should turn all my guns in at the next buy back event.

  9. #9
    Needs More Cowbell! Kyle's Avatar
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    Re: Short stroking AR-15... help!

    Quote Originally Posted by codygjohnson View Post
    I'm surprised you are running a 4.6oz buffer on a 20" barrel. I would have thought that was too heavy. When you say "standard spring" do you mean carbine or rifle? I'm almost positive you're running a carbine receiver extension and spring, but I thought I'd find out for sure.

    I would say, from what I've read here, that you're new gas block is more restrictive than the old one. You are running the heaviest carbine buffer available, so it's pretty likely that's the culprit. I would suggest you move back to a H1 (3.7oz) or a carbine (3oz) buffer.
    I am setup for carbine all the way through. Like I said I am somewhat new at this, I thought the heavy buffer may cause an issues but I was not sure, it makes sense. I stuck my upper on my buddies lower (he has the same buffer but it seems like he has a much lighter spring; it cycled a bit better but there was still some short stroking every few rounds.

  10. #10
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    Re: Short stroking AR-15... help!

    20" mil-spec barrels are drilled for m855 and other HOT military load ammo. Those ammo's besides creating more back pressure for a heavier projectile, also have higher pressures b/c of thicker brass and less case capacity than any commercial stuff you get from academy etc... The hole is undersized in general.. If you can run the hbuffer do it.. Your last gas block probably had a bigger hole.. it being dead center is important if the hole is smaller but also the coating on the new gas block might decrease the size.. Now people might be thinking a coating causing a problem? We are talking ar-15s here guys.. the smallest thing can mess up the cycle of the gun.

    Take it apart clean the gas tube end, check for burrs, use a drill bit in the gas block, also get a drill bit and do the hand turning on the gas port of the barrel.. These gas ports can get dirty.. Over time these gas ports do expand however.. Rifle length gas system is the furthest away from the bullet.. less power and the smoothest and helps reduce wear on the gun..

    Unless you like spending big bucks on ammo or can handload hot.. I would take the time to expand the gas port now while it is off.. Again we are talking a small amount.. Call the company and ask what they recommend.. Opening this port and keeping your HBuffer I think will give you exactly what you want and will cycle the 55grn UMC you get from academy..
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