Ruger SR762 mauling brass with suppressor

[Sieg]

I just received my suppressor and on the first test session using cheap PMC Bronze 147g (2780fps 24" barrel) I shot the first round with just the brake and the gas piston regulator was set on 2, gas adjustment range is 0-1-2-3. That piece of brass was fine and ejected at 4 o'clock, I installed the can leaving the gas on 2 and shot a few and ejection was at 2:30, switched to 1 and it was at 2 o'clock, on 3 it was at 3 o'clock. No failure to feed and extract noticed. I'm using 10 round Magpul Gen3's and the bolt locked back on both final round shots.

When I collected the brass, mostly which landed in grass, the brass necks were caved and the case body was showing a crescent impact from the rear of the ejection port. I only shot 19 rounds total, and the gun has 160 rounds total shot count all with the same lot of PMC 147g. I've saved all the brass and this mauling only happened with the suppressor.

Due to the hype of the new can and no feed/eject issues I didn't do the formal one round lock back test which will happen on the next range trip.

As a precaution I disassembled the gas system, inspected and thoroughly cleaned.

This is my first time shooting centerfire suppressed so I have no previous tuning experience with suppressed AR's. So what I'm looking for is if I need to modify/tune the system what is the typical procedure on AR10's?

Mauled brass:

Rear ejection port interior impact point

Due to flash over exposure on the deflector you can't see where the case mouths appeared to be hitting from midpoint and outward to the tip.

Is it related to spring rate and buffer weight? Bolt travel?

Any insight will be greatly appreciated.

 

[loveha]

That ejection map, pretend to see it in your hands. Now walk over to the garbage, and drop it in the can. Walk away and forget it exists.

Now that is out of the way, since you only have 4 options to limit gas, you may want to look into getting a couple more buffers H2 and H3.

Then do the one round at a time with the least gas possible.
If it still locks back with bad brass , move to a heavier buffer.
If it no longer locks back open one notch. Till it locks back again.
You are trying to slow down the buffer whilst getting enough gas to eject and lock. It's a cat and mouse game that takes time. One that is best done with the ammo you will count on most, not plinking rounds as those can be weaker and not have as much pressure.

Another possibility is your ejector spring is a beast. That can be solved with clipping a coil or trying a different spring.

Can also try a different buffer spring.
Sprinco springs is an excellent place for all things AR rifle springs. https://www.sprinco.com/tactical.html

 

[hlee]

You can also go to a fabric store and buy some adhesive backed hook and loop (Velcro) strips. Cut a small piece (square) of the fuzzy strip and apply it to the brass deflector where you see the brass marks. This will cushion the impact some and help with the case mouth deformation.

 

[Sieg]

That ejection map, pretend to see it in your hands. Now walk over to the garbage, and drop it in the can. Walk away and forget it exists.

Now that is out of the way, since you only have 4 options to limit gas, you may want to look into getting a couple more buffers H2 and H3.

Then do the one round at a time with the least gas possible.
If it still locks back with bad brass , move to a heavier buffer.
If it no longer locks back open one notch. Till it locks back again.
You are trying to slow down the buffer whilst getting enough gas to eject and lock. It's a cat and mouse game that takes time. One that is best done with the ammo you will count on most, not plinking rounds as those can be weaker and not have as much pressure.

Another possibility is your ejector spring is a beast. That can be solved with clipping a coil or trying a different spring.

Can also try a different buffer spring.
Sprinco springs is an excellent place for all things AR rifle springs. https://www.sprinco.com/tactical.html

Agree, to me it appeared the bolt travel may be too fast and far when suppressed. The ejector spring felt surprisingly stout when compressing with a punch. It may be worth finally buying a Wolff spring assortment kit I've considered for a long time now. It will compliment my 1911 spring assortment nicely.

I'll check Sprinco for buffer and spring options also.

The PMC was for bought for barrel/action break in and SHTF back-stock. I plan on reloading something close to FGMM 168g going forward.

Thanks for the input, much appreciated.

 

[Sieg]

You can also go to a fabric store and buy some adhesive backed hook and loop (Velcro) strips. Cut a small piece (square) of the fuzzy strip and apply it to the brass deflector where you see the brass marks. This will cushion the impact some and help with the case mouth deformation.

Thanks, I could also contact cement some rubberized gasket material on it..... but that's bandaging a problem. The gun functions flawlessly until the suppressor is installed. And after shooting it with the brake and suppressor it's a night and day difference. That thing kicked like a mad mule in stock form with no butt pad. Now it's a soft filthy mule.

I need to do more focused testing and narrow down the source(s) causing the condition.

The brass impacting and deforming the rear of the ejection port isn't good.

 

[hlee]

Thanks, I could also contact cement some rubberized gasket material on it..... but that's bandaging a problem. The gun functions flawlessly until the suppressor is installed. And after shooting it with the brake and suppressor it's a night and day difference. That thing kicked like a mad mule in stock form with no butt pad. Now it's a soft filthy mule.

I need to do more focused testing and narrow down the source(s) causing the condition.

The brass impacting and deforming the rear of the ejection port isn't good.

Sorry I was not so clear. My suggestion is in addition to the gas adjustments previously suggested. The brass will likely still be hitting the brass deflector, and will still get some amount of case mouth deformation. Cushioning the impact will help in this regard. 308 ARs are just hard on brass...

 

[Sieg]

Sorry I was not so clear. My suggestion is in addition to the gas adjustments previously suggested. The brass will likely still be hitting the brass deflector, and will still get some amount of case mouth deformation. Cushioning the impact will help in this regard. 308 ARs are just hard on brass...

Hard on brass may be a slight understatement.

There may be a bolt gun in my future! Seems like a decent reason anyway.

 

[Sieg]

@loveha Thanks for the SpinCo referral, this link clarifies the assessment process well.
Gas Mass and Springs AR Tuning

 

[mtrmn]

That buffer face looks like it has a helluva lot more rds on it than 160. That would lead me toward a stouter spring/heavier buffer as well. Might take a look at this site also. He fixed me up on my old Bushmaster BAR10 (Pre-RRA)

Slash's Heavy Buffers | Products

 

[Sieg]

FWIW - I 'blueprinted' the system components this morning in preparing for tuning after I perform a formal focused ejection test.

Buffer tube depth 7.75"
Recoil Buffer length 3.25"
Recoil Buffer weight 3.0 oz.
Spring length 13.5"
Spring coils 37
Spring wire dia. .071"
Spring coil spacing .29"

Recoil Buffer appears to be lightest one in the ranges I've seen: H2 4.4oz, H3 5.1oz, H4 6.8. DPMS Carbine buffer 3.8oz.

I made a quick trip to the range and collected this data. Left to Right column 1 = Gas Selector position, Column 2 Brake or Suppressor, Column 3 = All single round feed from mag, Column 4 = Ejection notes, Column 5 = Brass condition.

Brass from above, front three are the last. This is 147g 2780fps/2522lb-ft. 168SMK's is what I'm hoping to use.

At this point I'm thinking my first component change will be a stiffer spring rate vs a heavier buffer.

Determining if spring rate or a heavier buffer, or a combination of both allows the widest range of bullet weights while shooting suppressed is the challenge.

I wonder if the .223 version of this gun uses a gas selector with smaller orifices, that could potentially be a quick simple fix.

 

[Sieg]

Spoke with Ruger this morning and Sprinco, also emailed Odin Works about their adjustable buffer.

Sprinco first recommended a Red spring, he didn't hear me say I was shooting suppressed, when I told him suppressed again he recommended the heavier Orange spring.

Naturally Ruger wouldn't give up any pertinent info other than the SR556 gas regulator has reduced flow vs the SR762 regulator. For $35 I think it's worth a try. If it's too restrictive the orifices can be drilled out with carburetor jet drills to fine tune.

I'm pretty sure I can modify the OEM buffer with tungsten weights by shortening what feels like one long aluminum weight in it now.

My thought is keep it simple and control the gas flow causing the issue vs adding mass and heavier spring rates. Won't more moving mass and a heavier spring equate to more felt recoil?

Does my approach make sense?

 

[ChitownCopper]

Yes more felt recoil and will make your rifle nose dive

 

[Sieg]

Ordered the Ruger 556 gas regulator from Numrich today. ?

 

[Sieg]

I received the 556 regulator and measured the orifices against the 762 regulator.
556: .048 .070 .0905
762: .052 .082 .0895

Using the 556 regulator in position 1 (.048) shooting 168g SMK's w/ 43.5g of Varget resulted in a 2 o'clock ejection with a flat on the case mouth.

Not knowing the OEM spring rate makes a spring change a guessing game.

The SR762 OEM buffer is 3.25" that weighs 3ozs (AR-15 carbine). Verses the standard 2.75" length AR-10 carbine buffer.

Based on manually cycling the bolt the spring rate feels heavy compared to my AR-15.

Would an Odin Works AR-15 Heavy adjustable buffer be the best first move?