New rifle problems

[Heshin]

My new rifle build has been giving me fits since the first round, here are the specs.

Firebird Precision Lower

Geiselle Super Dynamic 3 Gun trigger

Ace Skeletonized Stock

DPMS Rifle Length Buffer Tube

DPMS Buffer Spring, and JP extra power spring

DPMS Rifle Buffer, and JP LMOS Buffer

Nordic Upper

Nordic 18" Barrel with Rifle Length Gas System

Carbon Arms Gas Block

Carbon Arms Handguard

DPMS BCG, and JP LMOS

BCM Gunfighter Charging Handle

Ammo used, WWB, American Eagle and hand load 55gr Hornady FMJBT with 25gr H335 at 2.225 (2850fps)

Basicly what happens is that I can shoot a stage or about 15-30 rounds, let it sit for about 15-30 minutes and pretty much have a single shot rifle for the next 3-20 rounds or until I re-lube. It will always eject the spent case but will not strip a new round or will jam it into the feed ramps.

What I have done so far, first the gas block was just a tad off center, re aligned and better but still haveing issues, tried a heavier buffer with full weight carrier, JP LMOS buffer with full weight carrier, JP LMOS carrier with heavier buffer, JP LMOS carrier with JP LMOS buffer (works the best of the above, ejection is at about 4-4:30) JP LMOS carrier JP LMOS buffer and carbine buffer spring (seemed to work better than with rifle spring). I have tried numerious magazines as well as the upper on a bushmaster lower and the trouble follows the upper.

I seem to be getting a bunch of carbon in the upper receiver and some on the exterior of the upper from around the barrel nut.

I am trying to figure out if I have an overgassing problem where the BCG is trying to extract the case while the pressure is too high and loosing momentum and is why the lowest weigh buffer and spring combos work the best or is it an undergassing problem caused by leaking between the key and the tube. I am just assuming that going to an ultra light buffer and bcg system is just a bandaid for an underlying problem.

I had a smith look at the barrel port and says there should be plenty of gas and actually though I should try a heavier buffer to slow down the JP LMOS BCG, tried it and that didnt do it.

Any ideas on how to get this going without tossing a bunch of dough at it?

[Chuck Anderson]

Does it lock back on an empty mag after the last shot?

[kurtm]

First off many gas blocks are set up to be spaced forward the width of a front handguard retainer ( Mark will be along with if his is set up this way, and this time I swear I will remember). If this is the case and you have the gas block bottomed on the barrel shoulder you are 1/2hole off and under gassed. You ARE NOT OVER GASSED!

If you ARE noticing gas coming out the front by the barrel nut, make sure there is no obstruction in the carrier key. Take a pipe cleaner and push it through the key into the bolt carrier...you will be able to see it enter the carrier if it is clear.. Make sure the key is tight!. One of these things is the problem.

[kurtm]

One other thought, make sure that if you have a carbine length butt stock you have a carbine length spring. I have seen this happen with an M4 stock and a A2 length spring.

[Heshin]

It only locks back on an empty chamber when using the lightest possible bcg and buffer system, and then only 85%.

Gas block is centered over gas port and there is no obstruction in the carrier key (just tested).

There seems to be carbon build up on the first 3+" of the gas tube from the carrier end.

[Heshin]

One other thought, make sure that if you have a carbine length butt stock you have a carbine length spring. I have seen this happen with an M4 stock and a A2 length spring.

Rifle length stock, rifle length spring. Though it operated better with a carbine length spring, probably because there was less resistance.

Edited February 7, 2013 by Heshin

[pyrrhic3gun]

Yep, sounds like it's just short strokin'. Check the gas rings on the bolt. Do you have resistance to the bolt moving in and out of the carrier? If no resistance, replace the rings.

Otherwise, open up the gas port in the barrel...or shoot hotter loads.

[pyrrhic3gun]

Of course, my previous reply assumes you have an undamaged gas tube and key in your upper.

[Lead-Head]

in get that the gas block is centered, but Kurt's point about making sure it is not completely up against shoulder of barrel is very important as well. Did you get a measurement of the gas port size?

Edited February 7, 2013 by Lead-Head

[benny hill]

Let me ask a stupid question. Are you lubeing a lot INSIDE the bolt-carrier??

[Heshin]

Everything is lined up properly, installed a new gas tube today since I was getting so much carbon in the upper. Cleaned an lubed everything and tested, shot 30 waited and shot 30. No malfunctions but would fail to lock the bolt back. Took the bolt out of the carrier as pointed out by Benny, and the CLP had cooked off. Lubed the bolt heavily with Mobile 1 and it was another 150 rds before it wouldn't lock the bolt back every time (sometimes it would). By the way, this is all with the full weight carrier and buffer and I am not getting the carbon build up in the upper with the new tube.

Benny, how wet should the bolt/inside of carrier be? This is my first non bushmaster and both of them would run dry, I guess not this gun.

[Alaskapopo]

Everything is lined up properly, installed a new gas tube today since I was getting so much carbon in the upper. Cleaned an lubed everything and tested, shot 30 waited and shot 30. No malfunctions but would fail to lock the bolt back. Took the bolt out of the carrier as pointed out by Benny, and the CLP had cooked off. Lubed the bolt heavily with Mobile 1 and it was another 150 rds before it wouldn't lock the bolt back every time (sometimes it would). By the way, this is all with the full weight carrier and buffer and I am not getting the carbon build up in the upper with the new tube.

Benny, how wet should the bolt/inside of carrier be? This is my first non bushmaster and both of them would run dry, I guess not this gun.

AR's run best sloppy wet. It keeps the carbon fouling soft so the gun can continue to work. If you run it dry the carbon fouling will build up and stop the action eventually. Run them dripping wet. The first shot blows out the excess. I also run 5W30 the same stuff as in my truck.

Pat

[fastshooter03]

Wolff Makes a reduced power buffer spring....which might work.

I use them with A2 length tube, carbine buffer, and spacer system thats lets me increase the spring pressure incrementally if need be since the spring is actually longer in the tube than it would be with a normal rifle length buffer.

Nick

Edited February 8, 2013 by fastshooter03

[pjb45]

JP has a humorous note about lube. Something like if you are not getting splashed by lube every shot, it is too dry.

[Chuck Anderson]

Sounds like you are under gassed. First thing I would check would be what Kurt suggested. How did you center it over the gas port? Got a pic of the gas block?

[Sudden Death]

Do you have a adjustiable gas block ???

[Heshin]

Sounds like you are under gassed. First thing I would check would be what Kurt suggested. How did you center it over the gas port? Got a pic of the gas block?

When I received the upper it was off center a tad, measured everything multiple times both side to side and front to back, then marked centers, shot and verified the carbon marks that it was indeed centered, no doubt there.

Ill try it in Sundays local match and hope for the best, hope I can sort it out soon as I have a ton of dough allocated on major matches this year and equipment malfunctions really take a toll on the mental game.

If its not sorted out, next step will be a new gas block (adjustable) and then up size the barrel gas port if that doesn't solve it.

[Chuck Anderson]

How big is the gas port now? I did have a barrel with an undersized port.

[Heshin]

I'm not a machinist, but the bit I have that fits tight measures .093

[Heshin]

Pics of block

[larry weeks]

Sounds like you have it worked out. Only other thing I could suggest would be to make sure your chamber is clean and smooth and not causing the cases to stick. I had a chamber that was slightly short and caused cases to stick which had the same result as short stroking. Found that with a headspace guage. A couple of turns with a reamer and everything was fine.

[Heshin]

Sounds like you have it worked out. Only other thing I could suggest would be to make sure your chamber is clean and smooth and not causing the cases to stick. I had a chamber that was slightly short and caused cases to stick which had the same result as short stroking. Found that with a headspace guage. A couple of turns with a reamer and everything was fine.

I did take an AR chamber mop with JB paste to the chamber just to be sure it was smooth, but will check out the head space today as well. Thanks!

[Griz]

One thing to try is using gun oil instead of motor oil.

AR-15s run best with a CLP. The "C" stands for Cleaner which in theory keeps the carbon fouling at bay.

In addition to not having the "C" component, the viscosity of the motor oil you are using is probably not ideal... It may be slowing down the bolt carrier and contributing to the short stroking. Even lowly Rem Oil would probably be better than motor oil.

Most overgassed factory rifles will function fine with the wrong oil, but a fast competition rifle tweaked right to the edge of failure will be less forgiving.

[3gungeezer]

in get that the gas block is centered, but Kurt's point about making sure it is not completely up against shoulder of barrel is very important as well. Did you get a measurement of the gas port size?

Looks like you are up against the shoulder to me, move the gas block toward the muzzle and try it then.

Edited February 8, 2013 by 3gungeezer

[Alaskapopo]

One thing to try is using gun oil instead of motor oil.

AR-15s run best with a CLP. The "C" stands for Cleaner which in theory keeps the carbon fouling at bay.

In addition to not having the "C" component, the viscosity of the motor oil you are using is probably not ideal... It may be slowing down the bolt carrier and contributing to the short stroking. Even lowly Rem Oil would probably be better than motor oil.

Most overgassed factory rifles will function fine with the wrong oil, but a fast competition rifle tweaked right to the edge of failure will be less forgiving.

My guns have ran longer with motor oil than they ever did with CLP between cleanings or re lubing. The problem with CLP is it cooks off too fast. Not saying CLP sucks but if you use it use it often.

Pat