308 AR Cycling Issues

[bruss01]

Ok, I am continuing to try to make progress on my first 308 AR.

My first problem was a bolt catch issue... solved with creative clearancing of the catch to compensate for a badly designed upper.

http://www.calguns.net/calgunforum/showthread.php?t=789831&highlight=308+ar

Next was an issue with failure to extract, cases stuck in the chamber. chamber was polished, low mass carrier replaced with full mass. Problem CHANGED to now 1 out of 3-4 stovepipes. Zero failure to extract.

Any suggestions? It's a 18"barrel, could a heavy buffer improve this? What should I be looking for?

ETA: Forgot to mention I'm using the JP Enterprises Silent Captured Spring.

[bruss01]

Still hoping for suggestions. The thing that leads me to think "heavy buffer" may be the answer is that switching from low mass carrier to full mass changed the problem, lessening the severity. Just looking for tips on narrowing this down, since I don't want to shell out 100 bucks for a heavy buffer if that's not likely to be the issue.

[buellster]

Sounds under gassed to me. The heavier the bcg, the more had you'll need to move it. Do you have an adjustable gas block?

[mrwetwork]

Any idea what the gas port size is ? That's a huge factor for .308 rifles...

[mrwetwork]

Also, are you using a DPMS receiver extension (buffer tube) ? If you're using the DPMS receiver extension make sure you're using a dpms buffer... if you're using an AR-15 receiver extension... you might have other issues.

[rally200]

I assume you bought doubles of all the same parts at the same time, as you built twins. I was sent an out of spec buffer spring once, I had similar issues. I went around for a while till I measured it. I'd measure your extension, spring and check your buffer weight, just to make sure, and then move on to more drastic changes.
I now check all parts to make sure they are in spec before starting a build.

[bruss01]

Any idea what the gas port size is ? That's a huge factor for .308 rifles...

It's a Ranier Arms 18" barrel so it's using whatever they are using. I believe it's this one. I don't see a gas port size listed.

Rainier Arms Select .308 Barrel - 18 Matte Stainless

http://www.rainierarms.com/rainier-arms-selecttm-308-barrel-18-ss

Specs:

Barrel Length: 18"
Gas Block Seat: .750
Rifling: Polygonal 5R
Stainless Steel: 416R
Feed Ramps: M4
Gas System: Midlength (DPMS Patern)
Chamber: .308
Finish: Matte Stainless - Bead Blast
Twist: 1X11
Thread Pitch: 5/8X24
Weight: 2 lbs 10 oz
Testing: MPI tested
Made in the USA!

[bruss01]

Also, are you using a DPMS receiver extension (buffer tube) ? If you're using the DPMS receiver extension make sure you're using a dpms buffer... if you're using an AR-15 receiver extension... you might have other issues.

Not sure how to answer this. I'll have to take a look at the buffer tube, it's a nice part but I forget the specifics at the moment.

[mrwetwork]

Can you tell me where / what part you ordered for the lower receiver receiver extension ?

[falbuff]

Check the gas block alinement if its not lined up it will not cycle.

[bruss01]

Check the gas block alinement if its not lined up it will not cycle.

Here's the thing, I think it IS cycling just fine... in fact maybe a bit over gassed for some of the components. Switching to the heavier BCG helped... no more stuck cases. An 18" is not terribly short but it is shorter than most 308 barrels.

I've heard of people having issues like this and a heavier buffer or heavier spring helping. I just would like to try to narrow it down and have a bit more certainty before I lay down $100 for a part and then find out it's not what I needed.

[xfer42]

I built 2 with no problems from hodge podge of parts.
16in carbine, with "A" post, generic AR six pos buffer tube, cheapest .308 BCG I could find.
24in rifle length, .960 aluminum gas block, chrome carrier, standard parkerized bolt (came as complete BCG), ACE ARFX AR stock (.308 buffer).

Both cycle fine and never needed tuning.

Based on the description, I would agree on maybe gas block alignment. Maybe even the gas block or gas tube. I would imagine if it were over gassed, it would sling that case out like an AK (provided you have a case deflector).

[kcstott]

I built 2 with no problems from hodge podge of parts.
16in carbine, with "A" post, generic AR six pos buffer tube, cheapest .308 BCG I could find.
24in rifle length, .960 aluminum gas block, chrome carrier, standard parkerized bolt (came as complete BCG), ACE ARFX AR stock (.308 buffer).

Both cycle fine and never needed tuning.

Based on the description, I would agree on maybe gas block alignment. Maybe even the gas block or gas tube. I would imagine if it were over gassed, it would sling that case out like an AK (provided you have a case deflector).

Over gassing can have the exact opposite effect and actually slow down the cycle of the weapon.

[phrogg111]

Yeah... if you're having cycling issues, don't get a heavier buffer.

BCG is "bolt carrier group" - i don't know why you'd get a heavier bolt carrier, or even if you can get one.

I had the problem that my AR-10 didn't cycle well after I first built it, too. I had to use a rubber mallet and a tool to get the bolt carrier out of the upper and pull the spent case out.

This is not a chamber issue. This is probably a break-in issue. The bolt and barrel extension probably lock incredibly tightly after a round is fired.

After I cycled the bolt a few hundred times, and managed to get a full 20 rounds through the rifle, it cycled flawlessly. I haven't had a jam since.

[Safra460]

If you are using the JP silent captured spring make sure to remove the stop pin in the buffer tube. This will allow it to fully push the BCG forward and prevent a light primer strike.
Talked to JP when I installed it in my LRP-07H and had similar issues. This should solve your problem.