Taming a .308 gas gun

fastex500

fastex500

Sergeant
Full Member
Minuteman
Apr 10, 2011
297
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50
Gaston County, NC
#1
So..... my Mega Arms build has come to a close and the load development and break in are in full swing. The weapon system is great, accurate and reliable so far, but the brass and moving parts seem to be getting beaten up. Here is my current setup:

MA-Ten with Troy 13.8" rail system
.308 20" 1-10 Lothar Walther barrel, rifle length gas system
Troy lo-pro gas block, standard rifle gas tube
Matching bolt in Fulton chrome carrier, JP internals
Standard Rifle length buffer tube, buffer and spring

So... I have developed a few mid 2600fps loads in Mil brass with 178 BTHPs. Running Varget, 4895 and RL15. All are good, 4895 more consistent, but Varget more accurate. BUT.... with all of them, the action is violent and the brass ends up with 2 vertical marks on the neck, ejector marks and extractor marks. Maybe I am being paranoid, but the brass looks beat to hell compared to my 223 gas gun brass.

I had purchased a Paladin Machine adjustable gas block (.875") to remedy this issue (in addition to the fact that I am waiting on form 4 for my 30 cal can)... but it would not fit under the Troy handguard. The only .875" adjustable gas block I can find is the Seekins, which is out of stock everywhere..... hence my move to the Troy LoPro.

My next look was at the JP extra power spring and a heavy buffer.

Thoughts? Or am I just being a brass nazi?
 
#3
Re: Taming a .308 gas gun

I am also "Brass Frugal."

Both a heavy "Slash" buffer AND a Tubb Carrier Weight System with the heaviest (tungsten) insert can help reduce brass abuse.

Your brass is typical -- the two marks on the case neck are from hitting the inside of the barrel extension between two locking surfaces for the bolt. You will also probably have a small dent in the side of the case where it hit either the end of the ejection port or the brass deflector.

The added dead weight will both delay bolt carrier rearward movement and unlocking, and slow bolt carrier group velocity. A heavier spring may or may not affect the weapon's cycling (a great big shove forward on the bolt carrier group during the feeding phase of the operating cycle).

You are probably also getting more soot on the cases than on your bolt guns as the case may start extracting while residual bore pressure may be fairly high (not quite as bad as with short gas tube DPMS AP4 variant carbines).
 
#4
Re: Taming a .308 gas gun

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Comes with the territory, I have a heavy buffer and spring on the way to help some. Hope it helps with the ejector swipes.

 
#5
Re: Taming a .308 gas gun

PRI's Lo Pro Adjustable is the one I use on my Troy rail and I couldn't be happier. It's almost like it was made to fit in there.
 
#7
Re: Taming a .308 gas gun

Sounds normal to me. Mid 2600s out of a 20" you are probably at max. I've tried weights etc and adjustable gas block makes the biggest difference, bar none. That or just drop your charge, 41.5 varget in LC brass should give you about 2550fps won't notice a difference until you try to really get out there at which time a 20" 308 isn't really ideal anyways.
 
#8
Re: Taming a .308 gas gun

I'm a newb on the site but I was, literally just, wondering the same thing with my MWS since I'm looking to get into reloads. Since I've never reloaded, I don't know what's acceptable or not. Heavier buffers and springs are great but it seems if you could reduce gas pressure it would help save abuse on the extraction and ejection of spent brass. I use an adjustable gas block on my one suppressed SBR upper and it works really well. Also, it should fit under the Troy rail.
http://www.syracordnance.com/
Works great on my BCM 11.5" 5.56 barrel and a SF 556-212.
 
#9
Re: Taming a .308 gas gun

Thanks for the reinforcement everyone. I assumed it was normal... but we all know what that does!

Bleaman, welcome to the forum! Great group here and you will learn a ton (I know I have). Thanks for the link to Syrac, and I have spoken with them before, but my luck.. they do not make a .875" adjustable block.

I'll take a look at heavy buffers on everyone's recommendation. Plus, it might be time to use the CNC to make my own lo-pro adjustable .875" gas block
wink.gif
 
#10
Re: Taming a .308 gas gun

I've had the same problems with loads using Varget and similar burning rate powders in my 20" R-25. Ar-Comp, IMR 8208 and H4895 are much easier on brass at least in my gas gun. For 175 and 178 grain bullets my gun really likes 40.9grains of H4895 in WW brass and 40.6 grains in Lapua brass both with 210M primers. Buffer springs do make a difference! These loads work great (between 1/2 and 1MOA) with the standard buffer spring and do not like the Tubb spring. I've been watching for a long time and you are right this is a great place to get good info!
 
#12
Re: Taming a .308 gas gun

I noticed 4895 was easier on the brass as well, and after reading a few old posts here on the hide, I saw why. Looks like Varget is a slower powder than 4895 and RL15, so the pressure builds up slower, thus resulting in higher pressures at the time of gas delivery to the tube and BCG. I've got a Tubbs CWS on the way, so we will see how she does.
 
#13
Re: Taming a .308 gas gun

I run TUBB carrier weight systems and their flat buffer tubes in all the AR10s, seems to reduce signs of excess pressure and doesnt beat the brass up so much. The AR platform is going to be hard on brass, it doesnt just trickle out of the ejection port, pretty violent process. foam tape or loop side velcro on the deflector helps with brass denting on ejection as well.

Kirk R
 
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