18in barreled AR is not fully cycling the bolt?

[NavyshooterM40]

While I was in AFG, I had an armory buddy build me an 18in SPR using a Spikes lower and Viltor upper. It has an 18in Walther barrel and DPMS hard chromed bolt carrier (AR type) using the bolt that came with the barrel. It is shooting single shot and has around 100 rounds thru the rifle. The bolt will cock the hammer and eject the round but does not go far enough back to strip a round.
The gas port hole in the barrel measures around .092in. The gas block is a PRI and shows no signs of leakage. The gas key in the bolt is not loose and does not show any signs of leakage.
I have installed a reduced power buffer spring from Wolf and have lubed the bolt until oil is dripping off it. Still no Joy?
Does anyone have any recommendations on a fix?
Thanks
V/r
CAPT1515NAVAIR

 

[Oodin]

Re: 18in barreled AR is not fully cycling the bolt?

The eternal question: will it lock back on an empty magazine after firing?

Is it ejecting strongly? Could it be a magazine issue?

Could check for burrs/residue in the buffer tube that might be hanging up the carrier.

 

[kilo7788]

Re: 18in barreled AR is not fully cycling the bolt?

Do you have a different bolt carrier to try? What about the action spring? Is it the proper match for the receiver extension? Buffer too large? carbine vs full rifle for both buffer and spring.

 

[Loopm5]

Re: 18in barreled AR is not fully cycling the bolt?

Things I would check if it is not a mag issue.

#1 gas rings should be staggered not all lined up, sound small but I had one last year we looked for 2 hours .

#2 check alignment of the gas tube in the upper receiver. Some times it is very hard to get the barrel nut lined up perfectly at the specified torque.

3# Recoil spring and buffer. (are they correct for your application).

Hope this helps

 

[Scottmilk9]

Re: 18in barreled AR is not fully cycling the bolt?

sounds like a lack of gas issue. make sure gas block is aligned perfectly, that is usually the problem.

Also try it on a different lower to see if your wolfe spring is too strong.

 

[Longbow_06]

Re: 18in barreled AR is not fully cycling the bolt?

Try changing your ammo ? I had some USGI stuff which nwas a bad batch and would short stroke the bolt.

Lee.

 

[Dtarget]

Re: 18in barreled AR is not fully cycling the bolt?

I had the same problem with Igman 5.56 in a 20". It was the ammo.

 

[Mark L]

Re: 18in barreled AR is not fully cycling the bolt?

What Mech1 said also check the mag. I thought first the gas hole was not the right size but .092 should be good. What gas system do you have carbine, mid or rifle. Do you have the correct buffer an springs? can you manually pull the bolt back and see that it wont go back far enough?

 

[deadly0311]

Re: 18in barreled AR is not fully cycling the bolt?

what length gas system are you running?

 

[BattleAxe]

Re: 18in barreled AR is not fully cycling the bolt?

If you're running an aftermarket stock make sure the stock bolt doesn't protrude too far into the buffer tube. The buffer will hit the bolt and cause this problem.

 

[zx1963]

Re: 18in barreled AR is not fully cycling the bolt?

Its a gas problem, .092 gas hole should be good for a mid length, as stated make sure the gas block is in the right place, also take a good look at your gas tube where it runs inside the carrier key. I have noticed some new gas tubes are not machined right in this area, they are undersized and will make you pull your hair out trying to find the gas leak! Also as stated throw another carrier in it and try it, it will eliminate the carrier group.

 

[k2peaker]

Re: 18in barreled AR is not fully cycling the bolt?

If after checking all the items that others have suggested (gas rings staggered, gas tube alignment, etc.), it sounds like you're 80% of the way to "tuning an AR for recoil" with the light buffer and spring. In competition ARs it's common to seek the holy grail of the softest recoil impulse. For example, check out JP rifles and the combination of low mass parts that they subscribe to (www.jprifles.com). You're close on that path.

On a 18" MSTN that I have, I wanted to lighten up the recoil impulse so I started trying a combination of parts. Similar path as you and having the "not cycling fully to strip" problem (assuming good, full power ammo). I finally ended up with the JP low mass carrier group, light buffer and spring, AND a PRI adjustable gas block (running pretty wide open). If you've eliminated the other variables/suggestions, I would suggest you go to an adjustable gas block so you can fine tune the amount of gas for cycling.
Note: even with my gas block wide open, I never could get the lightest carrier I could find (a pure Titanium one) running 100% -- the JP low mass was the best compromise that runs reliably for me. Note: when I shoot suppressed I usually have to bump up to a slightly heavier carrier -- a YM NM model.

Good luck.

 

[NavyshooterM40]

Re: 18in barreled AR is not fully cycling the bolt?

All,

Thanks for all the great input. I moved the PRI gas block about .050 toward the muzzle and it solved the problem. It looks like I might have blocked part of the gas port hole at its original position.

Thanks again.
CAPT1515NAVAIR

 

[triplecelectric]

Re: 18in barreled AR is not fully cycling the bolt?

I had the same situation and it turned out to be that the shoulders were not bumped back far enough while resizing my brass.