Need some help, 308 Gas Gun Reloads

[jrhtx]

Been reloading for 40+ years, yes I am old. Mostly pistol, bolt guns, and high volume 556 on a Dillon S1050. My 308 bolt guns typically shoot .5-.75 with my reloads. If they shoot this, I don't chase it.
I have been working with a LMT/MWS now for a year off and on and it still shoots reloads like a shotgun with buckshot. Factory barrel contoured by ADCO to lighten it up.

I can get factory ammo, FGMM and even the Federal Blue Box WallMart special to shoot about inch. I have tried Varget, RL15, and mostly IMR 4895 with 155 AMX, 178 AMAX, 168 SMK's, 155 Nosler Custom Comp, and just tried 165 Sierra Spitzer BT (for a hog load).

Chargemaster used to throw and checked with a Ohaus 10-10. CCI 200 primers, 1x fired Nato Brass, no crimp, typically loaded 2.820

I am still working on shooting technique for a 308 gas gun but damn, no reloads will shoot. What am I missing?????

 

[bruddah]

What's the twist and length of the barrel?

When was the barrel profiled? Since new or recently? Have you shot factory Ammo through it since the barrel was profiled (lightened)?

 

[bobke]

Have you tried using same bullet as factory loads that shoot well, loaded to same base to ogive length as that factory load? Shoulder setback about .002 less than fired rounds? I have an older GAP build Armalite with 11.25 twist Schneider barrel that shoots any 155 with Varget or 8208 very well, cold bore on. Sounds like something in the loading process not to same spec as factory rounds.

 

[jrhtx]

Started as factory 16", 1/10 chrome factory barrel. I had it profiled a couple of years back. Did not shoot it before profiling, but it was a new factory barrel. Barrel was cut to 14" and QD pinned to make 16.5". Crown was inspected prior to pinning and looked good. Wouldn't expect an issue from factory barrel.
Gemtech switchable bolt carrier, JP High Pressure bolt
Shoulders bumped .003-.004.
It will shoot factory ammo about an inch now, after profiling.
My reloading process is the same as my bolt gun ammo, just different brass. I picked up some new Winchester brass yesterday and am going to try that. Loaded on single stage press, Redding sizing and RCBS Completion seating dies, checking charges with balance scale, hand priming brass with RCBS priming tool, digital calipers with Hornady comparator tools (headspace & ogive).

 

[JCCinOhio]

I had the same problem... With FGMM I was getting ~.75-1" groups, but my reloads sucked. What seems to have done the trick for me was I started using an expander mandrel, and added a crimp. The expander mandrel I got custom from PMA Tool to be -.0035" from .308 (so it measures .3045"). So after some springback I'm getting about 3 thou neck tension. The crimp is with the Lee FCD, and I do maybe 60-65% of a turn (bit more than 1/2 turn). This brought me from couple inch groups to averaging about .6" groups at 100, with my best at about .3".

I was finding before that the bullets were slipping big time on chambering due to the mass of the BCG acting like an impact bullet puller. Try measuring one of your reloads for COAL, put it in your mag, then another bullet on top (don't need to measure this one). Then shoot the first one, extract the second and measure to see how much it slipped. I was getting a huge variation over about 10 times I tried this. Tightening up on the neck tension and adding a crimp seems to made the difference at the target.

 

[bruddah]

I had the same problem... With FGMM I was getting ~.75-1" groups, but my reloads sucked. What seems to have done the trick for me was I started using an expander mandrel, and added a crimp. The expander mandrel I got custom from PMA Tool to be -.0035" from .308 (so it measures .3045"). So after some springback I'm getting about 3 thou neck tension. The crimp is with the Lee FCD, and I do maybe 60-65% of a turn (bit more than 1/2 turn). This brought me from couple inch groups to averaging about .6" groups at 100, with my best at about .3".

I was finding before that the bullets were slipping big time on chambering due to the mass of the BCG acting like an impact bullet puller. Try measuring one of your reloads for COAL, put it in your mag, then another bullet on top (don't need to measure this one). Then shoot the first one, extract the second and measure to see how much it slipped. I was getting a huge variation over about 10 times I tried this. Tightening up on the neck tension and adding a crimp seems to made the difference at the target.

Good suggestion on testing the neck tension.

Also as mentioned, get some 175gr SMKs over Varget or IMR 4064. Try switching to Lapua brass if possible too.

 

[jrhtx]

I have a Lee crimp die. I will shoot a few to see if the bullets are moving and try the crimp.
Thanks