Gas Gun Help anyone?

G

generalist

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Hi everyone, I am new to this board and new to the benchrest sport. We have a local recreational 100yd indoor league I want to get involved with.

I have a DMPS LR-308 in 308win. I am fully aware that custom bolt guns rule here, but we have ot start somewhere, and this is the platform I have to work with right now.

In preperation for the league, I ordered and installed a 20" 12 twist Kreiger tube and competition 2# trigger. Obviously it is free floated.

Just starting to play around and hovering (best attained) at ~0.5" avg of 2, 5 shot groups. Not where I want to be.

This is with 150 Berger Flat Base. 168MK's were around 5/8 - 3/4".

I have only been using Varget (min to max loads) so far with match primers and new Nosler brass, Redding competiiton die set.

I also have only been running at a single COL so far of 2.80, but SINGLE FEEDING. This gives me 0.120 jump to my lands with this bullet. I am about to run a jump test at 0.000 (kissing lands), +0.005, +0.035, +0.070 & +0.105 jumps.

1. Can I try a run with jamming the bullet? If so, how deep. Single loading. Can I use the std min charge wt (40.5gr Varget per Berger) for these "jammed" rounds? Never tried it before.
2. If all runs well, where do you expect a gas gun like this to settle into? 1/4"? more / less? I love tinkering but Don't want to throw good money after bad either.
3. The optic is a Monarch 6-24x50 fin crosshair with Warne tactical mounts. Think my optic POI hold could be a limiting factor? Not sure how tight these scopes can hold POI.
4. Any other ideas I should try once done with the jump test?

Thanks all very much!

Nathan
 
Well, you already know the limitations of your platform, so with that disclaimer here is what I can add.

First: get some sort of adapter for your forend (accuracy asset) so that your forend will ride the bags flat. That round forearm is not condusive to accuracy.

Loads. Varget and RL 15 are good powders for that cartridge. If you can single load, find the OAL with the bullet is just touching the lands and play with jamming the bullet (try +.020" to start) and then try jumping .020". Somewhere in there you will find what the rifle likes.

Load the cartridges directly into the chamber with your finger, Don't let the bolt slamming home feed your cartridge. No wild rides for your cartridge are needed here.

Play with neck tension. If you don't have to load from a magazine, you can lighten the neck tension a bunch. Gauge the consistency of neck tension with your seating die. Bullets should go into the case with the same effort.

Those few items will get you started and provide you with enough variables for awhile.

Good luck.

Bob
 
Thanks, Bob. I will add jamming at 0.020" to my "jump test". Is is possible for the groups to shrink 1/4 MOA or more just my adjusting the OAL, knowing that I am jumping 0.120" now?
 
Nathan,

The factory rifle you have is probably fortunate with all the best reloading techniques, of occasionally shooting .5 inch groups.

A benchrest rifle it is not. To consistently shoot below .5" with a gas gun requires a bunch of action work, custom bbls, and some smithing from a really good gas gun doctor. Even then, .25 groups will be the exception rather than the rule with a 308.

Some of the custom AR15 match rifles in 223 can shoot .25-.35 inch stuff, but even they will not achieve the level of accuracy that a good bolt gun can muster. Many AR platforms are being offered in 6mm cartridges. There is where better groups will be found. Problem is that you will sink a bunch of money into the rifle and still come up against a limit on small group size.

Don't expect more than the platform can deliver. Accept the limitation and go have fun with the rifle you have. If you want to get serious, then look at what the serious competitors are using. That will be your best bet.

Bob
 
just to show you what you are up against...
you essentially have stock everything.
i have a krieger 1/15 twist bbl
the reamer was a 308 win BENCHREST..
bullets are BIB 134's
lapua brass neck turned/prepped/sorted
3" wide flat fore arm
36x luepold scope
custom trigger
this rifle has shot as small as 0.116.......can shoot under .2
and yes it is an armalite ar10 custom built.

you have a big uphill battle......
yes start at the lands and single feed...switch to the new imr 8208 powder....its very good in 308's

bob ,
what kind of ar10's do you have ?? what kind or ar15's ???
i have been doing benchrest work with my ar's for over 10 years....
mike in co
 
Ar-10t

mike in co said:
just to show you what you are up against...
you essentially have stock everything.
i have a krieger 1/15 twist bbl
the reamer was a 308 win BENCHREST..
bullets are BIB 134's
lapua brass neck turned/prepped/sorted
3" wide flat fore arm
36x luepold scope


custom trigger
this rifle has shot as small as 0.116.......can shoot under .2
and yes it is an armalite ar10 custom built.

you have a big uphill battle......
yes start at the lands and single feed...switch to the new imr 8208 powder....its very good in 308's

bob ,
what kind of ar10's do you have ?? what kind or ar15's ???
i have been doing benchrest work with my ar's for over 10 years....
mike in co
Click to expand...

Mike,

How much does your Armalite AR-10T weigh?

I had one awhile back and it was pretty heavy but never weighed it.
 
Thanks everyone, kind of what I expected. I will run the jump test, ck a couple of more powders and just jjump in to some matches and start enjoying the sport. I am sure I will be looking for a used custom bolt in 6ppc or 30br in no time! I will try to report back on what I can get this rig down to.
 
333smitty said:
Mike,

How much does your Armalite AR-10T weigh?

I had one awhile back and it was pretty heavy but never weighed it.
Click to expand...

depends on how much lead i put in it.....the t i shoot in a factory class, the custom i shoot in br.
mike
 
How would this 20" 12 twist 308 win do for f class if it will hold 1/2 moa for heavier bullets?
 
Last edited by a moderator:
Mike,

My Ar10 is a Scott Medesha custom built NRA Match Rifle. Krieger bbl chambered in 6mm XC. Medesha float tube. Modified Knights trigger, Adjustable butt stock by White Oak Precision. Carrier has an external charging handle. RPA and Riles iron sights.

I shoot the rifle at 200, 300, 600 and 1000 yds. It basically is the equivalent of a T2K that loads itself while launching 107 SMKs.

It won't shoot in the one's but pretty consistently in the threes/fours if I do my part. Off the bench is really the worst place to shoot it with that round forearm. On the ground, with a sling and irons is where you will get the smallest groups.

Bob
 
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