Bumfuzzled..AR not cycling...

[KYShooter73]

Swapped barrels on an AR, 300 blackout, 14.5in barrel, pistol gas port location, standard buffer and spring, .067ish gas port size which I think is about normal for pistol length. Port is properly aligned to gas block. Bold seems to rotate and close properly. Everything is clean and wet. Until fired, everything "feels" like butter. Lee 321-155 2r, powder coated, gas checked, 16gn of Lil'gun, sized .311. Should be running about 1900fps. Heavy - normal recoil, the round chambers and fires, but I don't think the bolt is moving at all. Could be a bit, but not even ejecting. Fired a few more loaded with plenty of W296 to cycle, but nothing. Case ejects easily by hand. Cases show some primer flattening. I see some powder fouling on the gas tube around the bcg end of the tube, so I know I'm getting some gas back there. This is a comp perm attached, supersonic only, no suppressor rifle for brush/hill country white tails and fun shooting.

The only thing I did was remove the .300blk 16in carbine ported barrel and gas tube and replaced it with 14.5 inch pistol length ported barrel with new pistol gas tube. Everything down to the gas tube roll pin is the same rifle that was working last week.

I'm stumped hard....this is a should-be-simple barrel swap. I need that one genius answer before I put this new barrel in the drill press and make a port I can drive a truck through. [smilie=2: Thanks!

[nhrifle]

I am leaning toward either the gas port being too small (had to open mine, 16" carbine length gas system) or the powder itself. I would start with trying a different powder, as the volume of gas produced during combustion can vary depending upon the powder composition. AAC developed this round using both AA1680 and H110, so I would suggest trying one of those before drilling out the port. If you do open the port, do so in small steps with plenty of testing after the modification. Might also be worth trying a lighter buffer or cutting a couple coils out of your buffer spring.

[tomme boy]

Not enough gas, or the hole is not where it is supposed to be. Here is a little chart that might help.http://farm4.static.flickr.com/3312/3639283889_ee25f9d8d7_o.jpg

First thing I would do is see if the port is in the right location. Blow air through the barrel to see if it comes out the gas tube. plug the chamber end and blow from the muzzle.

[300blk]

+1^
You can plug it with a spent blackout case.
16.5 I believe is what I am running with that same boolit, pistol gas port 8" barrel. Ejects with authority. If you have another gas block try that. Usually the gas lock and not the barrel is the culprit. If chrome lined, a peice of tp (white) in the chamber and a bright light at the muzzle will allow for a check of the port. Wish you all kinda luck.

[CATTLEMAN]

I worked for several months to sort out a 300 blk with carbine gas firing subsonic cast loads without a can, I eventually got it working great.

Things you may already know but I noticed and wished I had know in advance:

Make sure the gas tube is not obstructed I have seen them with a burr inside.

Hyper sonic loads tend to cycle a lot more easily the subsonic.

AR BCGs need to break in and often run better after a few hundred rounds, run the bcg wet with lube to help it get going.

I had to enlarge my gas port a lot (way bigger than yours). The adjustable gas block I bought was a waste on 300 blk because I was almost always under gassed and run it wide open all the time.

I was able to check and adjust the gas port alignment after firing a few rounds and reading the soot / residue on the barrel and gas block after dis-assembly. They were not optimally aligned and I had to adjust them.

Powder selection is CRITICAL. 1680 was the most likely to cycle in mine and one other maybe 5744 worked also. 110, 4227, lilgun never worked for me with subsonic loads.

The hole in the gas tube inside the gas block can also be matched to the gas block if needed.

I cut / weakened springs, lightened buffers etc but a light weight BCG was the real fix. With a low mass BCG I can use standard lower parts (buffer / springs) and get correct functioning.

Cycling is really tied to gas volume / pressure / timing in the AR platform, look for any pressure / volume leaks at the gas block, the BGC key etc and correct as needed. The little BLK case doesn't produce a lot of gas and it needs the AR to use it efficiently to run correctly.

Hope these tips help, since I got mine running, it is a blast!!!

[Blanket]

check your gas rings on the bolt, if they are shakey it won't unlock

[andremajic]

I would not alter the spring or buffer tube. Reason would be to keep it interchangable with any future uppers that you might use with it.

I'd have to measure my gas hole but from what I remember, my pistol length system had to be opened up larger than what yours is.
If it was my rifle however, I would prefer to exhaust other possibilities before drilling.

Do what the previous posters have suggested first.

If you open it up too much, you can still buy an adjustable gas block as a fix, but that is money that shouldn't have to be spent, if everything is done correctly.

[wlc]

I had close to the same problem with a newly put together 16 incher with carbine gas. It wouldn't cycle Rem 220 gr factory subs at all. I started loading a few different charges/bullet weights up to see what it would take to cycle and after hand cycling the action about 200 times, lubing really well and putting a touch of "grease" on the friction surfaces where the bolt rides it smoothed out and now has cycled everything I've put through it. Evidently it likes to be wetter than I started off with and also needed being worn in. I did have a jam with one load today with a Hornady 225gr. I think that was a function of OAL though as it was the longest load I tried and was rubbing the mag rib a bit too much.

[garandsrus]

I had a similar problem when i rebarreled an Ar-15. It turned out that the gas port hole wasn't drilled all the way into the barrel.

John

[Artful]

Have you tried factory ammo?

[grampa243]

my gas rings lined up one time. made even j words not work the bolt all the way..

powder plays a big part in cycle rate.

[KYShooter73]

Have you tried factory ammo?.

Of course not. Only ammo I buy is rimfire. Thanks everyone. Gas key is fine, bolt rings are fine, stoppered the barrel with an empty case, blew down the muzzle with bcg removed, plenty of air passing through, no air passes with bcg in place. I didn't try shooting it today, but I did take a couple weights out of the buffer.

[tomme boy]

From the reading I have seen, you are going to need to open the gas port hole in the barrel.

[KYShooter73]

Gentlemen....I have never seen this before. I believe it was Mooseman in the chat room that suggested it. It really shows the difference between knowledge and wisdom. You only get wisdom the hard way. THERE WAS A PRIMER JAMMED TO THE BEND OF THE GAS KEY ON MY BCG! Thanks everyone. Here is a new issue to check for when you have gas problems.

[tomme boy]

Would never had thought of that on a new build. Did you ever remember popping a primer?

[xacex]

I have popped primers and had them go into the FCG pocket, but never in a gas key. That my friend is 1/1,000,000, and would have baffled me for a good while.

[KYShooter73]

Ya, I've popped primers playing with my tinker-toy ar parts. The only thing new was the barrel and tube. This damnblasterded primer has cost about 300 bucks, because I bought the pistol port barrel cause I couldn't get the carbine gas barrel to cycle. I probably blew the primer when I was first working up loads with the carbine barrel. I've laid in bed weeks picturing the gas flow to the bcg to the buffer to the spring, back with the spring pushing the weighted buffer...enough momentum to strip a new round...etc etc.

So true...

94016

[Blanket]

Gentlemen....I have never seen this before. I believe it was Mooseman in the chat room that suggested it. It really shows the difference between knowledge and wisdom. You only get wisdom the hard way. THERE WAS A PRIMER JAMMED TO THE BEND OF THE GAS KEY ON MY BCG! Thanks everyone. Here is a new issue to check for when you have gas problems.It was just constipated