AR15 Upper Won't Cycle

[RDA 226sig]

Bought a new AR upper from a vendor at the gun show, mated it with a Rock River lower and was ready to rock......but not really. It is a heck of a single shot but I had somehow envisioned a bit higher cycle rate. When fired the bolt just sits there with no attempt to cycle. It appears that there is no gas passing into the gas tube and therefore no pressure reaching the bolt carrier. (It runs very clean though...just not very fast.)

What is the best way to verify the alignment of the gas block and gas tube with the barrel? What is the best way to test the flow of gas through the system at the workbench?

 

[JD0608]

is this a factory built upper or did someone build it using rra parts.? you using your bolt and carrier or did upper come with one.? if its a home built job it will probably be best to take the front sight or block off. you can pull sight,block and gas tube off together. try blowing through the gas tube and see if air passes through ok. if this is a home build, more than likely the problem is with the gas system. if gas tube pin is in place the tube could still be up side down - with gas port facing up.. i woud start by taking the tube out of the sight and make sure it is in right.

 

[degunner]

it is a direct impingement gun and not a piston gun? My buddy bought a piston kit and had problems with it cycling and I had problems with a regulated gas tube cycling problems.
like jd asked is this an upper thrown together or is it a factory upper? is the front site block canted at all? I mean even a little, also if the fsb is fwd or aft on the gas port you will not get enough gas to cycle the bolt...canting the fsb can do the same thing.
those I would look at first, there are several other things
are you using factory ammo? under charged reloads can case cycling problems too.
let us know how that went.

 

[RDA 226sig]

The upper is of the direct gas variety. It was assembled from parts by the gentleman that sold it to me. I pulled the front sight block along with the gas tube and it appears tp not have been properly aligned. Headed to the range to see if my realignment has solved the issue.

 

[1911Tuner]

Check to see that the bolt carrier key is tight and properly staked. If it's loose, short cycle is the result.

Take the bolt out and see if there are three little rings there...like miniature piston rings.
Like piston rings, the gaps should be staggered.

Make sure that the bolt moves freely in the carrier.

Make sure the gas tube is getting into the hole at the front of the carrier key.

If all those things are good, either the gas port in the barrel isn't aligned with the port in the front sight or the tube itself is plugged.

 

[Taurus 617 CCW]

Stupid question but did you check to make sure they guy put a gas tube roll pin in the gas block? If he forgot to pin the gas tube in place it will absolutely cause cycling problems. You could also check to make sure he didn't install the gas tube upside down (I've seen it happen before). Keep us informed on what you find.

 

[RDA 226sig]

Took the offending weapon to the range this morning and fired 20 rounds in single shot mode and there is no indication that gas is reaching the carrier. If you fire with the dust cover in the closed position the bolt doesn't even move far enough to open the cover.

1. The gas tube engages the carrier.
2. The rings on the bolt are staggered.
3. There is a roll pin retaining the gas tube in the sight block.

It appears that gas is getting into the sight block but not into the gas tube based on powder residue coming out between the barrel and the block.

 

[longdayjake]

That carbon buildup on the gas block is normal. You may have something inside your gas tube. They are easy to take out and replace if you need to. I wish I could get my hands on it and see myself.

 

[degunner]

is the gas tube obstructed?
Do you have a standard A2 triangle type fsb or do youhave a bolt or screw on type?
Is the gas tube the correct length?
Is the gas tube a normal type meaning no valve at FSB end.

The gas tube should go from the fsb through the delta ring/barrel nut/split ring assembly into the reciever and should go into the reciever and be close to the bolt carrier assy.
i am not sure if it should make contact or not i am sure others here would know.
reason I ask is if you have a rifle length barrel ~20" and a shorter tube you probably wont get any gas to the bolt carrier. Similar issuses may result for carbine/midlength barrels gastubes improper matches but am not real knowledgable of these issues.

 

[falmike]

Sounds like as mentioned above, gas tube 180 degrees out of alignment...i.e. upside down. The hole must face the barrel.....remove BCD and CH, remove gas tube roll pin, slide gas tube towards receiver....if hole in tube is facing you rather than the barrel, that was the problem....if so, rotate tube so hole faces barrel, and reverse the previous steps.

Good luck!

Mike

 

[RDA 226sig]

The winner is....the gas tube had been installed 180 drgrees out which explains the total absence of gas reaching the carrier. Hopefully I can get back to the range later this week and try it again but I am confident that was the problem.

Thanks for the help.

 

[guntech59]

Make sure to check the gas tube/carrier key alignment after you reassemble it.

He may have had to "adjust" it to get it to fit together right during the first assembly.

Glad you got it fixed.

 

[Taurus 617 CCW]

Gas tubes can be installed upside down if one does not pay attention. It can be a frustrating thing to diagnose too because it appears to be correct. FYI for all who experience gas problems with the AR, insert a rubber stopper in the breach end (chamber) and blow down the front of the barrel feeling for air at the back end of the upper receiver. If you can't blow or it is severely restricted then you either have an obstruction in the gas system, the gas tube is upside down, or the gas block is not aligned properly on the barrel.

 

[Riss]

Hmmm. Go find a schematic for the upper to make sure that you have all the parts you are supposed to have and they are all in the right place. If the bolt does not move at all, either the gas tube hole is misaligned, obstructed, or you are missing parts.

 

[BUGUDY]

I had this problem one time, it was a spring in the lower that was not aligned properly. The prongs on the spring must be resting on the pin correctly in the lower,. Someone here will know what I am talking about and elaborate.

 

[RDA 226sig]

The problem was that the gas tube was installed upside down by the factory (or whoever assebled the upper)... I will go talk to the vendor next time the gun show is in town. Anyway, I turned the gas tube to the correct orientation and reassebled the upper making sure everything was aligned. Took it out to the range yesterday and it works perfect now.