I'm looking for some advice on my brand new 9" 300 blk gas piston upper.
I've taken it to the range three times and am getting discouraged. I've tried everything and can't get it to cycle on subs.
I'm using a Spikes Tactical lower and stock AA upper with their light bolt carrier.
Here's a pic of the setup.

http://s6.postimg.org/oq8l6hz0x/image.jpg


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And here's the ammo I shot. None of them cycled. All shot and ejected but not one chambered after.

http://s6.postimg.org/c04cter2p/image.jpg


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The rifle runs great other than it won't feed/cycle the next round using subs. Supers worked with and without a suppressor attached.
The 5 position gas port was wide open and I tried everything from an H2 buffer to a standard carbine buffer. I even tried a buffer where I removed the weights and stuck a wooden dowl for a spacer which made it very light. Again, it would not strip the next round off the magazine.
I even replaced the buffer spring with a standard carbine spring. I think my original spring may have come with my LWRC stock for use on my LWRC 10.5" SBR and was a little bit longer.
I tried several different mags that all work on my 5.56 SBR. So I ruled that out as well.

The first time it didn't work I called AA and they told me to pick up a Carbine buffer and that it would run for sure. Obviously that did not work.
Could I have an issue with my gas block? I've got another email in with Cory but won't hear back til next week some time. Out of office outoreply.
I'm not really excited to blow a lot of expensive ammo just to get this upper that was sold as a complete EVO upper to work.
I was told that the new ARC MVB stock would also work but at this point I'm not ready to drop $400 on something that should have worked out of the box.

I wonder if the 9" uppers didn't work well since they're not offered anymore on their website?  Maybe I just got a lemon?!?  While I wait to hear back from Adams Arms I figured I'd throw it on here and see what sort of advice I could get.

Thanks all!

Have you tried a different magazine? missed that part


My experience with Blackout and pistons are that the gas port on "some "  BO barrels need to be drilled out to work probably with a piston but that is a last resort. If you did not build this one do not touch anything on the upper.  I would first think the block might be misaligned . Call AA again and tell them what you did to try to get the upper to run. They will probably bring it in and let them deal with alignment or drilling out the gas block.

I tried the ARC stock/ syrac piston combo on one of my 300 sbr builds. Could not get it to work. I wanted the stock more than the piston. The piston now lives on 556 rifle

BTW once you get the blackout running start reloading. Its cheap to load blackout and fun. BO is what got me finally into relaoding

Right on, I'd like to get into reloading.  First things first I guess.
Interesting about the ARC. It is nice quality looking stock.
I think you're right, I wonder if something isn't misaligned. It is a complete upper by AA. I won't mess with it until they can give me some direction.

Hey sir this is Garrett, i work with adams arms support team, if you could send me an email at [email protected] i can assist you with this instead of going back and forth on the forums i can directly help you out. Hope to hear from you so we can work on resolving your issues you are having with your rifle.

Take care,
Garrett
Adams Arms

Wonderful, thx Garrett.  Email coming your way.

Bunyan,

I hope you and Garrett are able to tune your rifle and gas system so that it is also reliably shooting subs suppressed. If you achieve this please let the forum know what was done.

DB

Will do.  Obviously I would like to be able to shoot supers and subs reliably.
Isn't that what the gas port is for?  Close it down and you should be able to shoot supers. Open it wide up and it should cycle subs reliably with a can attached.
I'm going to go shoot this morning after speaking with Garrett from AA.  I want to make sure it's not hyper cycling.
I'll be sure to report back.
The guys from AA's were great on getting back to me and trying to decipher what's wrong from my perspective.  Worst case I have to send it back to them and they'll make sure it cycles on subs and supers.
The 5 position gas block is a bear to switch btw. I put some slip2000 on it to ease it up a bit.  Very hard to move the adjuster without marring the small adjuster knob.

Update -
Was able to make it to the range and took a few short slow-mo videos with my iPhone.
Supers will cycle at 50% gas with a can attached.
Supers will not cycle at 25% gas with can attached.

Now to the subs -

They just won't cycle in any variance of gas settings and several different ammo (208/220 grain) along with the can on.
I shot at 25%, 50%, 75% & 100% gas.
If I remember right (will have to check my short videos) the 25 & 50% gas did not eject the spent casing.
75% & 100% gas ejected the spent casing but wouldn't strip another round off the magazine.
In slow-mo you can see the little Adams Arms symbol on the bolt carrier not quite cycle as far back as when shooting and cycling correctly with the supers.
Guess my only option is to send it back to AA and have them work on it.

I may try and include a link to the videos if anyone is interested in that.
I don't know how to embed a video here.

@ Garrett, an e-mail is coming your way later today.

Keep us updated. Pistons are tricky on blackout with all the variation, that's why I'm surprised AA offers them. Hope they get it worked out and it was simply a misalignment of the gas block.

I ended up sending the upper and lower back to AA for them to test.  Great guys to work with.  I am sure they will get it to work properly.  
Standing by...

They have some of the best CS I've ever dealt with.

As for your issue I didn't see where anyone asked what buffer you were running.  The trick to getting them to cycle is light components.  If you have the light carrier but are running a +2 heavy buffer you're defeating the purpose of the lightened carrier.

Otherwise you're down to the recoil spring being too heavy or there is a gas problem somewhere in the upper, be it the port too small, the block clogged or leaking somehow, or the piston in a bind due to inexact alignment.  Whatever it is they will get you taken care of.  The 10.5" I have runs like a sewing machine with the XLP and lightened components.

Good to hear your 10.5" is running smoothly.  AA did mention that a 9.5" or even longer barrel would cycle supers and subs more reliably.  Maybe it's just that .5" that's not getting it done.  
I ran everything from an H2 down to a buffer with all the weights removed and replaced with a wooden dowel.  Standard carbine buffer spring.  
No go on either one of them with subs (208GR & 220GR).

They received my 300 last week.  I expect it will be a few days before they can get to it.  Hope to hear from them soon.

AA guys are top notch and take care of it. They have gone wayyyy above and beyond for me in the past, only people I will buy piston retrofit kits from.

Since you have a 9.5" barrel, the dwell time short.
You need to ream out the gas port hole to make the gun function.
I have familiar situation with my 7.62x39 10.5" barrel, after reamed out port hole  to .132" my rifle function flawlessly.
Hope this help.

Thanks for the comments guys.  The rifle is still at AA and I'm sure they're going to make it run reliable.  
I'll update once I get it back in hand.

Update -

AA sent my 300 back and replaced the bent gas rod.  
I have not had a chance to shoot the rifle yet but will update once I get a chance.

After sending in my complete rifle to AA they returned it pretty quickly after replacing the bent gas rod and aligning it and giving it a once over.  They did not open up the port. They test fired it with a few subs I provided and packed it back up and sent it back.  
I finally made it out to the range and test fired it.
Good news is 220 grn subs cycled without any issues with the can on.  208 grn subs did not cycle.  I tried Gorrilla ammo and another brand I can't recall.
I guess that's as good as it will get.  I know 300blk is finicky but I know people are getting good results with it.  Maybe 300 and piston systems just aren't meant to be.
Maybe I'm expecting too much?  
I'll keep shooting 220grn subs.  Maybe it just needs more of a break in period.
I guess if I could have it my way I'd like it to cycle 208grn with a wide open gas port and maybe 220 on setting 4 out of 5.
Then there's the problem trying to switch the gas port setting. Very difficult to switch it without marring up the switch or the rail.  
Thanks to AA for replacing the bent rod and servicing the weapon.

It has nothing to do with piston systems ....it called barrel length and dwell timing on a 300 black out round.

I had a similar cycling issue on my 10.5 with 223. I'll have to once over it to make sure it's not a bent tube and it's aligned. After that maybe I just lightly thought the port. Thanks!

Try a JP silent capture spring and it will help with those subs

Thx, I've heard about that as well.  Might give it a look down the road if I run into issues again.
So far 220grn are running fine.

Good write-up, analysis, and solution Bunyan.
Thanks for the legwork! Great to see the fix.

All that info is good. Yes, 300 Blk is finicky when you start varying from the DI, 16" barrel with supers.
I had an ok write up on this that I posted on 300 Blk but that site is down ATM for some reason...

My last built and test points that I can remember ATM:

Weapon specs:
300 Blk, 8.5" Hbar, pistol gas, AA piston kit with XLP block and light BC with POF roller cam pin, Mil Spec lower, buffer tube, Silencerco Omega when suppressed.

Ammo Specs:
1. Super - Off the shelf, Bulk SAA, 147 gn FMJ, MV of 1750-1850 fps actual.
2. Super - 150 gn Sierra FMJBT GK, 20.5 gn of A1680, Fed SR 205 primer, COL 2.140"
3. Super - 150 gn Nosler, BST, 20.5 gn of A1680, Fed SR 205 primer, COL 2.150"

4. Sub - 220 gn Nosler, CC, 11.5 gn of A1680, Fed SR 205 primer, COL 2.260" - MV of 1026 fps
5. Sub - 220 gn Nosler, CC, 11.5 gn of A1680, Fed SR 205 primer, COL 2.230" - MV of 1058.6 fps
(Ammo testing specs: ambient temp - 65-68F at ALT 3675' ASL.)

Testing was done with focus on BCG lock back and fired by a human (not in a test fixture)

Points of modification:
Piston Drive Rod gap tolerance -.020" to .015" (although nominal as I didn't see much difference between .015" and .020")

Buffer to -H (no internal weights)

Buffer Spring - carbine spring with 3.5" removed. To get clinical you will need to measure spring rates. Wolff springs are an option and so are Tubbs. standard is 11lbs in battery and 13.5lbs compressed.
I did not have my rate gauge available when I chopped my spring so I had to guess and use POE in .5" increments. Keep in mind that you are changing the overall rate by cutting. Generally springs get stiffer when cut. Spring science definitely plays a part and there are many factors that I won't dive into here.
I am in the process of producing a factory spring with a 300 bulk piston rate for both Subs and Super fire.

Drive Rod Spring - can be changed with spring of different rate. Ace hardware. (AA did not recommend this change)

Gas Port to .125"

Gas Block - port opened at south by 30 degrees and polished for flow and alignment.

"With these types of set ups I would suggest having spare, wear parts such as springs as modded items are usually not as resilient."


Conclusion:
Depending on my specific load all Supers locked back at half gas both suppressed and unsurpassed. Recoil was not overly forceful.
Most Sub loads locked back with suppressed fire and full gas. Some sub loads failed to lock back but still stroked enough to strip and chamber the next round.

Mag/load testing is still on going as subs with large C.O.A.L.s put the bullet tips uncomfortably close to the inside of the mag and many hang up once more than 10 rounds are loaded.

hope this helps by giving some reference points.

DK

Enrje,

Thx, that was very insightful. Sounds like you have access to some nice equipment.
I recently picked up a Maxim Defense CQB stock with their proprietary JP silent capture buffer spring.
It ran great on my 10.5" 5.56 LWRC gas upper but wouldn't cycle subs on my 300 blk AA 9" upper.
Supers ran fine but even suppressed shooting subs with gas wide open wouldn't cycle (not that I was expecting it to with the standard JP buffer spring).
I'm going to contact Maxim Defense to see if they have a lighter JP spring. Maybe try the 9mm buffer spring?

All this to say that I really like my 5.56 gas piston upper but not sure I would do a 300 blk in gas again.

Have you changed out the buffer weight?  I noted an H2 early in your posts, but browsing through the updates I didn't see that change (I may have missed it if you did).
A lighter buffer may improve the cycling for some of the subs..

Yes, it's up there somewhere. I took all the weights out of a buffer and stuck a wooden dowel in it and it runs pretty decent but it still hangs up on some subs with a suppressor and gas wide open.
From what I understand even DI run systems have issues with certain ammo.