AA 19.5" upper troubles

[topcaat1]

Long time visitor new member.

I recently purchased an AA 19.5" Advanced WPN System upper.
Would not feed after fireing.
Would not lock bolt to the rear after last round(occasionaly bolt carrier would lock back on the follower with bolt protruding over the magazine).
Occasionaly would rechamber fired case.
Occasionaly would try to feed a round and end up jammed with the bolt contacting the case about a third of the way up from the case.

The lower was a new Rock River Operator and the ammo was both factory Hornady 123gr AMAX and reloads (123 gr AMAX, 27.5 & 28 grs 8208, CCI#41,@ 2.245").

Took the rifle into the shop where I bought the lower. Their first thought was there was to much gas leaking from the gas block/tube after noticing the fowling in that area after less than 50 rounds. They also suggested a heavier buffer which I did buy with no luck.

Returned the upper to AA with their repair form. Did not notice at the time but when I printed it out a lot of the info was cut off in the right margin. Recieved the upper back in less than 2 weeks! The form that came with it did not mention any of My concearns with the gas issue only that the costomer reported feeding and cycling problems(due to the repair form printing issue).
AA polished and blended feed ramps and test fired with 100% function.

Back from the range. Tried the RR Operator and a RR Tacticle lower with previous mentioned ammo and 123gr Lapua reloads with 29.5 grs aa2520, and CCI #41 primers @2.26".

This time the rifle would function most of the time with Hornady 123gr AMAX. Failed to feed twice out of 15 rounds. 5 Magazines of 3 Rounds each. Failed to lock back on empty mag 5 out of 5 times.

IMR 8208 no change from before.

Accurate Arms 2520 cycled 100% but failed to lock bolt on empty Mag.

I think its a gas issue. Placed a strip of paper towel under gas tube by the gas block and it ends up about 2-4 inches under the hand guards after one shot with obvious carbon fowling on it. Is that to much leakage?

Or is it because I am useing CAR lowers on a 19.5" upper.

Have had 100% reliability with all the above mentioned ammo and the RR Tacticle lower
when used with My SABRE 18" upper.

Its hard to maintain focus with these problems but have mannaged to keep all groups under an inch with majority hovering around .5". Would really like to get this thing up and running.

What should be My next step?

Sorry to be so long winded but have noticed You Guys are very thorough in Your questioning and annalysis.

Thanks.

[LRRPF52]

What mags are you using? If 17rd CProd, try 10rd or 25rd. You might also need to send it back with the full explanation. Sounds like you have a gas system issue from your post, but who knows. I would look at the alignment of the gas block, and determine what material it is. I avoid Aluminum blocks for this reason, but I don't think AA uses them either, and they usually loc-tite their gas blocks.

Also, if you haven't, properly lubricate your upper with Slip2000 along with bolt carrier raceways, cam pin hole, and lightly on the outside of the lugs. A dry AR15 does not usually run, but since your Sabre runs, this might be negligible.

Also, check that your gas tube isn't binding against the carrier key. With those loads, you should have very positive lock, even with milder charge weights.

[topcaat1]

Thanks for the feed back. I am useing AA mags both 10 and 25 rds. It has an AA low profile gas block on a Shilen 19.5".
It's a little dry in the pictures from today(still within specs.) but trust Me it was wet with CLP for the first two outtings.
[attachment=498][attachment=499][attachment=500][attachment=501]

[Drifter]

Might be an issue with the gas system as you suspect, but seems to me that the result is short-stroking. Your 2nd and 4th pics are clues, and also that it happens more often with 8208 powder, which burns relatively fast. And 8208 causing short-stroking would be more prevalent in your rifle-length 19.5" versus your midlength 18", just as you're experiencing.

Not always a reliable gauge, but your ejection pattern could also be a clue. Further to the rear, around 4:30 or 5 o'clock, suggests weaker ejection versus spent cases going out at 3 o'clock. This could mean a gas system issue, or perhaps too much weight and resistance in the buffer system.

Instead of a heavier buffer, I suggest trying a lighter buffer, buffer spring, and / or BCG. If you don't have alternate parts onhand to test, cutting a couple of coils from a buffer spring might be the least expensive way to experiment.

Gas leak isn't uncommon, and yours might be excessive, but reducing the resistance in the setup might allow a little more rearward travel of the BCG when the weapon is fired. Factory 123's and 123 using 2520 will be more likely to work versus loads using 8208.

If it worked on AA's lower, the difference could be between your lower and theirs. If they're using a lighter buffer and / or spring, it would explain the difference in performance. Other variables between their results and yours might be ammo and magazines. And finally, if the system is right on the edge of reliable functioning, it will be more reliable without the added weight of a heavy optic and mount.

Try it without the scope and see what happens. Otherwise, lighten up on buffer and spring. And I wouldn't waste ammo using 8208 until you get reliability with slower powders like 2520 or factory loads.

[topcaat1]

Once again, thanks for the input. That was My first thought when I took it in to the shop where I bought the lower. They however said no if it was not the gas block leaking then it was more likely unlocking to soon and not building up enouph pressure. Thats when they suggested the heavier buffer. Think I'll start cutting on one of My extra springs.

[Bill Alexander]

The system uses a rifle length gas system. The timing for the unlock is near perfect but the pressure dwell at the port is at a minimum, ie there is not a lot of margin for error.

We did test fire the upper with a variety of rounds including Wolf, Hornady and AA. The test lower for this would be a standard A2 with full stock and rifle buffer. Function was 100% but the feed was erratic due to a burr on the feed ramps. Hold open was checked as this was mentioned. All rifles are tested in a fixture that has a gas spring retardation.

Do not start cutting springs. There are two components to the correct operation of this weapon the preload value and the compression rate. move either out of the correct range and you can damage the weapon.

[Bill Alexander]

Did this as two posts because the forum is messing my replies about. If you keep having problems call and we will look at the complete gun for you.

[Mutt]

LRRPF52 has some really good suggestions ........

Are you running it wet or dry?? This problem sounds an awful lot like short stroking do to being dry/lack of lube.

If it is a fairly new AR, then you deffinitely need to run it wet. Spray down that BCG right before you fire a string. Keep it really oiled well ... at least at first.
And, if it is new, the parts do need time to break in. When brand new, the parts still have rough spots on the finish etc .... give it some time to smooth out.

The other thing I would suggest would be to run factory ammo for 50 - 100 rounds (Wolf .... it cycles the easiest). If you are not having issues with factory ammo, then it is your reloading that is a problem and not your rifle. If you still have issues with the factory ammo, then it may be your rifle. I never break in a new rifle with reloads.

[LRRPF52]

Did this as two posts because the forum is messing my replies about. If you keep having problems call and we will look at the complete gun for you.

Bill,

How did you take time out of your insatiable quest for endless profits and Grendel market domination to stoop to one of your lowly customers? I can't believe it. Must be your shop warden...



Rupert (Hal): "Great news ladies. Sales are up, soooooo...arts & crafts just got extended by 4 hours."

Employee: "My fingers hurt. Can't I use the dremel now? She's had it already since last night after tee and biscuits. Doing these feedramps by hand is killing me."

Rupert: "What's that? Your fingers hurt do they? Well you just pulled extra gas spring retardation fixture system trouble-shooting duty. Anybody else's fingers hurt?"

Ahhhh, capitalism...I love the smell of cranky employees in the morning!

Merry Christmas daddy!!!

LRRPF52

[topcaat1]

Took the gas tube off last night and applied some permatex thread locker to the tube just short of the gas port. Also in the hole where its pinned to the gas block after noticing more carbon fowling there. Trying not to get any in the barrel port.
Had 100% success with the Hornady factory loads. My hand loads cycled 100% but still only locked back on the bolt carrier not the bolt its self. Having not checked in with this site, I proceded to cut 2 coils short of the factory AA spring from a rifle length spring. Hand loads are now 100% also.
After hearing from Mr. Alexander guess I will go back to the factory spring and work up a new handload(hate that, love8208).
Is AR Comp on par with 2520 as far as burn speed? If so will this possibly help?
I dont think the permatex is going to hold up long term, any thought?
I appeciate everyones input. Never thought I would hear from the boss man himself. Thanks.

[Drifter]

As long as the buffer spring isn't cut excessively short, I would think it would be okay. Doesn't seem to be an industry standard anyway, as both rifle or carbine springs from different sources might be different lengths and have a different number of coils.

AR-Comp is a little slower burning versus 8208, and will tend to be less likely to short-stroke.