AR wont cycle [Archive] - Militaryfirearm

franks71vw

01-26-2011, 12:51 PM

Question what can cause an ar not to cycle. have two AR's one with a collapsable stock other solid stock with different stock buffers. Each of the uppers have a 20" barrel standard parts etc. However the collapsable stock rifle will fire but not chamber a round. Swap uppers and it works fine...
Swap bolt carriers and no rechambering.. now swapped barrel with everythign else being the same and rifle cycles.. Also a new gas tube was installed???? Anyone take a crack at this...

rep30cal

01-26-2011, 12:57 PM

yellowhand

01-26-2011, 07:39 PM

Check the gas tube as well, Q'Tips ends have been known to get in there and block up the gas flow, but as noted prior, gas rings is a good bet too.

imarangemaster

01-26-2011, 09:14 PM

If the shorty lower is having trouble, it may be the recoil spring. I had an M4gery that defied logic in its FTE and FTFs. I replaced the spring with a USGI M4 spring and it solved it for me. Apparently there was a slug of aftermarket springs that were way to heavy.

HKILLER

01-26-2011, 09:22 PM

U said both barrels are the same?

dcs12345

01-26-2011, 10:55 PM

If you are having trouble with the one certain bolt carrier not rechambering then that carrier assembly probably has the gas ring splits lined up. Take out the assembly again and make sure the splits in the gas rings aren't in a line, if they are turn them to different spots so they are staggered. Also make sure that area is clean, carbon and or grime can collect there and make the bolt drag causing it to short stroke.

That is a myth, a bolt will function with the gas rings splits lined up just fine. I have seen bolts work with just one ring.

Op, did you build the upper that isn't working? Check to see if the gas block is lined up properly. If it isn't over the gas port on the barrel, it will cause your rifle to short stroke.

Evilblackgunsrfun

01-27-2011, 02:57 PM

i had trouble with with my bushy varmintor , i bought two 5 round triple k mags and neither mag would function/feed right on the second round.
bushmaster, tapco, and the various other mags i have all work fine in all my bushmaster ar's , i thought it might be just the varmintor doesnt like the triple k mags, but they dont work right in any of my ar's or my buddies dpms

Perro Del Diablo

01-27-2011, 03:22 PM

i have personally witnessed a M16 with cycling problems start working again with new piston rings - I know for a FACT that the rings do affect cycling. Not sure about the holes lining up affecting anything, but if the rings are worn, this will cause you headache.

anothing thing i have seen that will make a m16 short stroke is a loose gas key. I saw a new in box bushmaster refuse to cycle - took the bolt carrier out and found the gas key wobbled - tightened the screw and it worked perfectly after that. Needed restaked

have you replaced the gas block with one of those clamp on kind??

franks71vw

01-27-2011, 03:39 PM

guys I swapped entire bolt carrier and bolt from one upper to the other and it still fails to feed. Gas tube was then replaced and still ftf... so only thing left was the barrel. kept everything the same and it runs now with out an issue.... so why would a barrel cause it to FTF???

rep30cal

01-27-2011, 04:07 PM

That is a myth, a bolt will function with the gas rings splits lined up just fine. I have seen bolts work with just one ring.

Op, did you build the upper that isn't working? Check to see if the gas block is lined up properly. If it isn't over the gas port on the barrel, it will cause your rifle to short stroke.

Not to start an arguement but I have tried this with an Eagle Arms AR, with the splits lined up the gun would not cycle completely. I took that exact same carrier group with the splits lined up, put it in an Armalite AR and it cycled fine.
These were identical A2 20" rifles.

imarangemaster

01-27-2011, 05:35 PM

Evilblackgunsrfun

01-28-2011, 04:51 AM

+1 to imarangemaster , the obstruction can be as little as a burr left in the gas port passage hole in the barrel under your gas block, because some of these companies are pumping out ar's really fast and it may have been overlooked
or the gas block has a unfinished hole in it or a obstruction of some kind, or just not lined up right

franks71vw

01-28-2011, 05:08 AM

well what should I do run a thin drill bit down the hole or??? I dont have any reamers or ways of deburring from the inside of the barrel??

Evilblackgunsrfun

01-28-2011, 08:49 AM

small drill bit would be ok, just be extra careful not to go into chrome lining on other side of barrel , you could slide a piece of round metal stock in the barrel or a old gun cleaning rod

spectre

01-28-2011, 08:51 AM

who makes the barrel? as stated above the gas port might be undersized or have a burr. if you think you have narrowed the problem down the the barrel i would definitely think it was that.

franks71vw

01-28-2011, 09:15 AM

Barrel is mArked DCS I am guessing Double Star??? I will run my sets of drill bits and then see which is the largest bit that fits inside of it and report back..

agalindo

01-28-2011, 11:29 AM

who makes the barrel? as stated above the gas port might be undersized or have a burr. if you think you have narrowed the problem down the the barrel i would definitely think it was that.

I would also suspect the gas port size. Did you remove the fsb when changing barrels? FSB might be off center also.

franks71vw

01-28-2011, 12:09 PM

yup swapped everything and it works on the other upper....

agalindo

01-28-2011, 01:33 PM

yup swapped everything and it works on the other upper....

Gas port would be my guess then.

Sampson1986

01-28-2011, 02:01 PM

Gas port would be my guess then.

My guess, as well.

spectre

01-28-2011, 02:22 PM

After Going through everything possible, it ended up being a small burr inside the barrel extension( from DPMS)and it was causing just the slightest bit of drag on the bolt lugs. I took the dremmel sanded it smooth and it worked perfect, I only realized it because i looked and seen a shiny spot on a new bolt and went from there. that little problem caused me one hell of a head ach! everyone keep that one in mind

found the above on another forum might check it out also.

wandering_ronin

01-28-2011, 04:40 PM

I know this will sound silly, but did you check the gas tube installation? I helped out a friend of mine trouble shoot a "single shot" AR, and it ended up that the gas tube had been installed upside down at the factory. No gas was getting into the barrel from the gas port.

franks71vw

01-29-2011, 05:40 AM

Ok ran a 3/32 bit through the hole .0937 and it did feel a bit tight but ran it through. Gas tube was installed correctly as it is short stroking.... lets see what happens now...

97th Signalman

01-29-2011, 09:23 AM

That is a myth, a bolt will function with the gas rings splits lined up just fine. I have seen bolts work with just one ring.

Patrick Sweeney, author of at least four books on the AR, agrees with you. He writes that the necessity of misaligning the gaps in the three gas rings is a myth.

Evilblackgunsrfun

01-29-2011, 07:58 PM

frank, if the other things dont help,you might have to buy a new gas block for it.
there might be a chance that when they drilled/machined the gas passage in your gas block, that the bit didnt go in far enough in on one end to make a nice big open gas passage in the bend inside your gasblock ,and it ended up being onley a half or less open hole.
or were the drilled gas passages meet, one hole was drilled off to the side, front, or rear alittle , again not letting it have a nice open and free flowing hole.
its pretty much the same thing as turning the gas system almost off on a fal