AR10 feed/ ejection issues when suppressed

[mzvarner]

I have an Aero uppler/ lower/ and BCG w/ WC 20 inch barrel/ M5 Carbine buffer kit. I have a Superlative Arms AGB, and have tried all the adjusments. It functions as it should unsurpressed with FGMM and my reloads. When I add my Sandman-S it has issues with reloads (155gr Palma MK, 46.1gr Varget, Hornady brass, CCI primer), every 3rd or 4th shot will stove pipe. This sometimes includes a double feed.

Not sure where to go next to diagnos the issue. Of note the WC barrel had to be sent back to have the gas port opened up. This was before the suppressor.

 

[msgriff]

I would try a heavier buffer. Aero uses a 3.8oz. Slash's and KVP have 5.6oz 308 short buffers, KAK has a 5.3oz. Heavier than those, you would have to change out your receiver extension to a intermediate/A5 length and use a extra heavy AR-15 carbine buffer and rifle length spring. Are you adjusting your Superlative in bleed-off or restrictive mode?

 

[NHPiper]

I had the same issue when I built my first AR-10. Get a slashes extra heavy (XH) buffer and it will solve all of your issues.

You need to slow down the bolt speed.

Heavy Buffers | Products | .308 Carbine

 

[mtrmn]

I know there are plenty of these guns out there that run reliably as is, but there are a lot that don't. Yours and mine are of the latter group.
Check out this thread:

PSA PA10 (308) Experiment

Sooo I wanted another 308 rifle, and was pondering back and forth between going Aero, PSA, or buying something used off here. My financial priorities do not align with mid to high tier 308AR/AR10's so under $1500 but closer to $1000. This would not be precision focused and will wear a 1-4/1-6...

www.snipershide.com

I'm sure there are more on here.
You probably will never get the gun to work properly until you get that sub-standard recoil system fixed. The buffer's too light (probably ~3.8oz) and the spring is most likely too weak for a 308. Also check the length of your gas tube, possibly too short.

I went through basically the same thing just recently with my PSA 16" build. Faxon 16" pencil bbl. 0.750 gas journal with a 0.093" port. Adjustable gas block. Sticking with the original AR15 buffer tube, I installed a Kaw Valley Precision 5.6oz buffer (2.5" long to work in that buffer tube which has a 7" internal depth) and a Sprinco Orange buffer spring. This made it perform admirably without my suppressor. Soon as I installed my suppressor the problems started again and it was not reliable at all at any gas setting.
When I decided to go even heavier with the buffer, I found that I would have to go with the longer Armalite/Vltor-length buffer tube with a 7-5/8" internal depth. This allows the 308 to use a normal-length (3.25" long) buffer.
Here's the easy button for that: https://www.eurooptic.com/Armalite-AR-10-6-POS-Receiver-EXT-Kit.aspx
That kit will come with a H3 AR15 carbine buffer, which weighs ~5.4oz. This may fix all your problems without going heavier.

I bought a different XH buffer with a 308 rifle spring from Heavybuffers.com which weighs 8.5oz.

Heavy Buffers | Products | XH AR15 Carbine Buffer

This wound up slowing down the bolt too much and I started experimenting with different weights by mix/match swapping out of the internal weights until everything worked suppressed/unsuppressed. Finally settled on 2 tungsten weights and 1 steel weight in the XH buffer to get a weight of 7.6oz. It now runs smooth and reliable with very little recoil. I only have to make a simple adjustment to the gas block to go from unsuppressed to suppressed to duplicate the good performance. It was a long and frustrating road to get it all to work properly, some of it self-inflicted. YMMV

 

[DangerRanger]

you have tried totally shutting down your gas block while shooting suppressed and there is no difference to it being totally open??

 

[mzvarner]

I ended up ordering the heavy buffer and spring combo above. I will update once installed. I will also test the gas block in the extremes of each position, because i dont recall how many clicks i attempted. The Superlative arms block has a lot more adjustments than i expected.

 

[mtrmn]

I ended up ordering the heavy buffer and spring combo above. I will update once installed. I will also test the gas block in the extremes of each position, because i dont recall how many clicks i attempted. The Superlative arms block has a lot more adjustments than i expected.

Which heavy buffer and spring combo did you order?

 

[mzvarner]

Which heavy buffer and spring combo did you order?

I went with the CAR-10 buffer and spring. I only have the 7" buffer tube, and would like to not sink a bunch more into this rifle other than upgrading glass.

 

[bfoosh006]

Correct me if I am wrong, but isn't that 46.1gr of Varget w/ 155gr a really stiff load for a gas gun ?

That load combined with a suppressor's back pressure, could be the main culprit.

How many rounds have you fired through the firearm ?

LFAR's seem to benefit from a longer break in period.

 

[mzvarner]

Correct me if I am wrong, but isn't that 46.1gr of Varget w/ 155gr a really stiff load for a gas gun ?

That load combined with a suppressor's back pressure, could be the main culprit.

How many rounds have you fired through the firearm ?

LFAR's seem to benefit from a longer break in period.

You maybe right. I looked on Hodgdons reload site, and for service rifles they recomend a max of 44gr!! I do not think that my manuals specify service rifle vs bolt gun, so I think I just worked up to a good group with the max load being 47gr. That is kind of a bummer, as I just loaded up another 50 to test fire with the new spring/ buffer. I guess I need to pull these and rework a load? That being said, it still does not function reliably suppressed with FGMM suppressed.

I Have about 500 rounds through this platform. Those are a mix of reloads and FGMM.

 

[mtrmn]

Here's what Lyman says. I normally trust them but this does look a little extreme for ARs. Also even though they used an AR10 for testing it had a 24" bbl. Not too much help when you're running a 16 or 18.

 

[mzvarner]

Here's what Lyman says. I normally trust them but this does look a little extreme for ARs. Also even though they used an AR10 for testing it had a 24" bbl. Not too much help when you're running a 16 or 18.

Interesting. The Nosler and Speer manuals both also claim a max of 47gr. My rifle has a bull Wilson Combat barrel on it. I did have 1 blown primmer last time I took it out, and when de-primming, the pockets felt a little loose. Guess Ill pull these rounds and work it back up.

I looked over my notes and I think what I was trying to do was push a 155gr 308 as close to 3,000 FPS. In my ballistic app this shows a trajectory similar to my 6.5CM shooting 140s, and used bolt gun data.