308 gas gun loading

[jlorenzo]

Starting to feel like I'm struggling a bit.
20" Krieger M110, JP HP bolt, Aero M5 enhanced upper and handguard
Aero M5 lower, Larue MBT2S.

Small base die, bumping .004", Fed brass and CCI 250s. Trimmed on a Henderson.

The 169s show promise and the 175 Noslers as well. Looks like I need to back down on powder charges very slightly across the board. I also kind of suck at shooting a large frame gasser. I can shoot half minute with my bolt guns pretty regularly.

Shooting off a Harris and Protektor F class rabbit ears rear bag. PRS lite stock. Some of those fliers are me fighting with position. (Off a concrete bench), I did notice shooting prone things tightened up a bit.


Any thoughts, currently just loading everything to max mag length, haven't tried many powder charges but I would've thought with the Krieger I'd have some nice clover leafs with something at this point.

 

[jlorenzo]

Some chrono data

 

[Fuj]

Pull the Harris and run the gun on bags. Tighten the equation up a bit
for load testing.

 

[whatsupdoc]

Forget the loads concentrate on controlling the trigger. One tip is to make sure the trigger is held to the rear until the entire cycle is complete and then you release your trigger finger and feel the trigger reset.

Dont force the shot, if you feel twisted behind the rifle stop and reset.

Those groups are not that bad I have seen a lot worse.

Watch her trigger finger.

 

[ELR LVR]

You might try 43.0 of W-760 with bullets in the 175 gr range and work up from there
175 TMK's work great.........
I tested these against 155's and 168's and the 175's came out on top for long range consistency.
That load worked great on several different 20-22 inch AR-10's I developed loads for
(I had a group of friends that all wanted to shoot their 308 AR-10's out to 1000 yds but didnt know much about load development)
I arrived at 44.0 grns
all guns Shot 1MOA or less with this load testing out to 700 yds
2 of which actually shot great out to 1200 yds
45.0 did not help much
going higher got worse
This powder also has a nice smooth recoil impulse
velocity was around 2450-2500 if I remember right (16 Moa for 600 yds)

 

[padom]

I have a 20" Krieger 308win I built on a matched MEGA Billet receiver set... JP BCG and SLA AGB... SLR handguard.

On a Atlas bipod and rear bag it shoots 0.5moa or less...

175 SMK
43.4gr Varget
1xLC brass
CCI LR

2647fps

https://imgur.com/23Ew4y0

 

[XTR]

Making a gas gun shoot tight is different for sure, just because it’s a name brand barrel doesn’t solve any of several other things. Upper to lower fit, trigger, and the barrel fit in upper come immediately to mind. (Not to mention load development or the Harris bipod someone else mentioned. I’m sure you have thought of that.

 

[BHP9]

Another powder to try is IMR4064. I've had the best luck with that powder.

 

[padom]

Another powder to try is IMR4064. I've had the best luck with that powder.

Excellent 308win powder but I've found is much slower in a shorter barrel 16-20" compared to H4895 and Varget but still very accurate.. IMR4064 is my go to 308win powder in my 24-26" bolt guns

 

[mic2377]

Long time gas gun shooter here, in both the AR-15 and AR-10 variations.

I think your loads a probably a touch hot, but certainly not dangerous. You are already on top of tweaking that. With my more mild gas gun loads I would typically see velocities in the 2650-2700 range for 150 gr class bullets, and 2550-2600 in the 168's. They seemed to stay in tune better and not beat the gun or brass up.

As for shooting technique, you need to drive the gun much more through the entirety of the recoil cycle, with a consistent grip, shoulder pressure, and follow through as it cycles. Limp writing these, or shooting free recoil, just doesn't work like a bolt gun. You are probably doing this better unconsciously when you are shooting prone. Prone shooting is also probably helping you with the bipod. As a rule AR-10's are tough to shoot from bipods as they can bounce inconsistently. Bags are the way to go for absolute accuracy (from the bench at least).

I think with these tweaks you will have it nailed. That being said I still wouldn't count on constant 1/2 MOA groups... If you can get a consistent average of 3/4 MOA for 5 shots between different days and conditions that be actually quite good.

 

[lb-ft]

My AR groups cut in nearly half when I stopped putting my hand fully around the grip, keeping my thumb in the right side of the grip and gently pulling the rifle straight back with just my middle, index and pinkie fingers.
Felt weird at first but dang if it didn’t produce results for me.

 

[jlorenzo]

I have a 20" Krieger 308win I built on a matched MEGA Billet receiver set... JP BCG and SLA AGB... SLR handguard.

On a Atlas bipod and rear bag it shoots 0.5moa or less...

175 SMK
43.4gr Varget
1xLC brass
CCI LR

2647fps

https://imgur.com/23Ew4y0

42gr with the Nosler 175 cci 250s and fed brass was beating up the brass a little bit, I wonder why your gun can take so much more powder. I do have my Superlative arms gas block all the way open though, carbine buffer tube, sprinco orange spring and small 2.5" 308 buffer.

 

[jlorenzo]

Long time gas gun shooter here, in both the AR-15 and AR-10 variations.

I think your loads a probably a touch hot, but certainly not dangerous. You are already on top of tweaking that. With my more mild gas gun loads I would typically see velocities in the 2650-2700 range for 150 gr class bullets, and 2550-2600 in the 168's. They seemed to stay in tune better and not beat the gun or brass up.

As for shooting technique, you need to drive the gun much more through the entirety of the recoil cycle, with a consistent grip, shoulder pressure, and follow through as it cycles. Limp writing these, or shooting free recoil, just doesn't work like a bolt gun. You are probably doing this better unconsciously when you are shooting prone. Prone shooting is also probably helping you with the bipod. As a rule AR-10's are tough to shoot from bipods as they can bounce inconsistently. Bags are the way to go for absolute accuracy (from the bench at least).

I think with these tweaks you will have it nailed. That being said I still wouldn't count on constant 1/2 MOA groups... If you can get a consistent average of 3/4 MOA for 5 shots between different days and conditions that be actually quite good.

I think you are correct about all of that. I would be happy with a consistent 1 moa.
Have you ever found groups tightening up seating farther back from max mag length? I agree gas guns seem to do better with lower charges, not beating themselves up. I'm dialing everything back a little. My only frame of reference for 308 so far has been a bolt gun that could take a lot more powder. I also may need to try some more springs and buffers. I was hoping to get the 155 smk shooting because I have a pile of them and they feel nice recoil wise, more controlled. Will be shooting inside 1k most of the time anyway.

 

[padom]

42gr with the Nosler 175 cci 250s and fed brass was beating up the brass a little bit, I wonder why your gun can take so much more powder. I do have my Superlative arms gas block all the way open though, carbine buffer tube, sprinco orange spring and small 2.5" 308 buffer.

I run an Adjustable gas block in combination with a JP SCS with their tungsten weights and spring pack. I tuned my buffer wjth different combo of weights and springs along with tuning the AGB to ensure my bolt wasnt coming back and ripping brass out the chamber before pressure subsided.. this is usually what beats up brass in a large frame gasser.. my brass looks excellent.

 

[Wildcats]

You might want to try RL15, worked very well for me in my KAC SR25 a number of years back.
In my M1A Supermatch RL15 with the 168BTHP 40.5-42 gr depending on the weather,it was very accurate.
The SR25 shared a similar load. with the 175s i was loading with IMI 308 match brass at the time. .

 

[mac86951]

Id recommend a BOB Sled for load work-up and mag feed after you're near a haply load for function testing.

Gas Tube touching barrel nut?

otherwise, looks like its shooting; and just as picky as most ive seen. Even with your JP HP Bolt; you may find the next lower node to be smoother overall, just my observation that my AR doesn't like similar nodes as my bolt.

Good luck!
-Mac

 

[distinguished]

As someone already said, loads look a bit warm for a gas gun. They may work great in a bolt gun but not in a gas gun. Back off a full grain -a grain and a half and work back up until it groups. The 41.8 gr w/ 175 looks good to me, maybe try the same load with 168's. 42.8 w/ 155's.

 

[cbrown1050]

42.2 grains of IMR4064 with a 175 grain SMK hammers in my Wilson Combat AR-10 out to 800 yards.

 

[Buttstock-TX]

Powder burn-rate is important to accuracy with gas guns. I've used 4064, Varget and RL 15 with a lot of success in different actions. AR Comp is the best powder I've used in an AR 10 type rifle with bullet weights from 168 to 175 grains.

 

[jlorenzo]

Backing things down, gonna to try more with the 169s and I have some 2156 Palma 155s on the way to try, along with the regular 2155s. Got some Starline small primer brass also.