Rifle groups well @ 100, but not at range?

[sawgunner2001]

Can anyone explain why my 20", GA Precision barreled, DPMS LR-308 will shoot like this at 100 yards:



But when fired at 200 yards, groups like this:



The rifle does this with every load combination I've been able to throw at it. I've tried Varget, H4895, 178 Amax, 175 SMK, 155 SMK, Winchester brass, LC Brass, and most combinations of each. If it matters, the groups pictured were the result of an OCW test I did last weekend where I found the "accuracy node" to be 44.5gr Varget.

I'm *mostly* confident it isn't me. I developed a load for a previous rifle (it was a bolt action .243) that I could CONSISTENTLY fire <.5MOA groups with most <.25 MOA at various ranges out to 800 yards. This leads me to believe that my handloading techniques and shooting techniques are not to blame. It is possible I suppose that the switch to a semi-auto is giving my shooting a hard time, but my 223 caliber precision AR consistently shoots <.75 MOA, so I don't know what gives.

I'm gonna take off the NXS 3.5-15x50 mounted in a Nightforce Unimount and replace it with a Leupold MkIV 4.5-14x50 thats mounted in a Burris R.E.P.R. and try it again next weekend. I've already checked to make sure that all the mounting hardware is tight to no avail, but maybe I got the one Nightforce that's broken. If that doesn't fix it, I feel the only thing left to do is rebarrel.

 

[Drock]

Just a thought but have you tried 168gr smk? My rem 700 .308 only likes the 168s no other weight seems to group well past 100 yards. I have tried 155s all the way to 180s and it's magic number is 168gr. Like I said just a thought.

 

[sawgunner2001]

How many rounds do you have down the tube ?

Not sure. I'm (at least) the 3rd owner of this rifle, and I'm starting to wonder if this isn't why.

 

[tipper]

If it's off-hand it's you

 

[sawgunner2001]

If it's off-hand it's you

These were fired from the drivers seat of a moving vehicle. Isn't that how everyone does their accuracy testing?

No, these were fired prone with bipod up front and bag in the rear.

 

[trailrider121]

Here are Dan's ocw charges for 308 win:


.308 Winchester using Varget
155 grain bullet, 47.8 grains
168 grain bullet, 46.0 grains
175 grain bullet, 45.0 grains (an all around favorite)

 

[BCP]

I had this happen and it was a bad barrel combined with a poor optics setup.

One thing to consider is sample size. Lets say for an argument that it'll put 20 rounds into 2" at 100 yards. However if you shoot say 2 groups of 5 each at 100 with a break in between you might luck out and get a couple 1" or better groups. Then you go shoot at 200, 300 and get 1.5-2MOA and wonder what is going on.

A borescope could really tell you if it's the barrel. Have your handguards been removed? Maybe loose barrel nut? Then check optics mounting and make sure it allows a repeatable cheekweld.

 

[sinister]

Not sure. I'm (at least) the 3rd owner of this rifle, and I'm starting to wonder if this isn't why.

Maybe find a gunsmith with a borescope and look at the throat and crown.

 

[sawgunner2001]

I had this happen and it was a bad barrel combined with a poor optics setup.

One thing to consider is sample size. Lets say for an argument that it'll put 20 rounds into 2" at 100 yards. However if you shoot say 2 groups of 5 each at 100 with a break in between you might luck out and get a couple 1" or better groups. Then you go shoot at 200, 300 and get 1.5-2MOA and wonder what is going on.

A borescope could really tell you if it's the barrel. Have your handguards been removed? Maybe loose barrel nut? Then check optics mounting and make sure it allows a repeatable cheekweld.

Although I agree with you about the sample size and the law of probability etc., this rifle consistently shoots like this. I don't think I've EVER seen a group beyond 100 yards be less than 1 MOA with most being 2+. I removed the DD 762 Lite Rail once to remove some material from the gas block. I did this because the gas block was coming in contact with the rail when the bipod was loaded with decent pressure. I just removed the rail again to check the barrel nut which *seemed* tight, but I don't have a DD barrel nut wrench to check for certain.

The optic was positioned on the rifle to give repeatable cheekweld. I just removed the optic (and mount) and replaced it with my Leupold MkIV for the next range session.

I'm not sure if there is a gunsmith local to me that would have a borescope. Most folks around here shoot pistols and that's who the gunsmith's cater to. If it fails to shoot better at the next range session, unless there are any decent solutions posed here, I'm gonna forego any borescoping and just rebarrel. Then the question is gonna be which caliber, how long, and which brand...

Maybe find a gunsmith with a borescope and look at the throat and crown.

Could the crown get f'ed up when it's being protected by a muzzle brake?

 

[sinister]

Depends how it was crowned.

 

[Kilmore]

Parallax, rifle bore, loft.

 

[Speedster00]

Im in the same boat I believe. I have a new DPMS LR-308 light which has a 24" stainless target crown barrel on it. So far I haven't found the recipe that it likes. Im lucky if I get2 MOA out of anything put through it yet. I have a friend with darn near an identical DPMS shooting sub MOA all day with cheap 150gr loads.

 

[Frank]

308 gas guns are harder to shoot well than a bolt gun. I'd also change my target to something I could center up on better, Say a black square or circle with a white center just big enough to be sure the reticle is precisely centered. May just be my old eyes need all the help they can get. Good luck and keep us posted on your progress.

 

[RTH1800]

Check the crown for carbon buildup.
Semi auto is more demanding and the weak link shows up more at longer ranges. Do you have a good shooter locally you could have shoot and see if he gets the same result?

I would not rebarrel until the cause was pinpointed. You will be more upset if you do so and still have the problem. Have you contacted GAP? They could diagnose and re barrel as well as anyone. Might be a simple fix??

 

[Unknown]

I would think that difficulty seeing the target easily is the problem. If you can't easily see/resolve the target at which you are shooting, the group size will suffer. I would suggest trying a target where it is much easier to center your reticle onto. One of those targets with the four squares that are about 2" square around the center would come to mind. That way, it will be easier to properly center your reticle onto the target.

I also found that with my Leupold Mk 4 scopes, I had difficulty resolving targets in the red/orange end of the light spectrum unless some kind of colored filter was used. My groups did the same thing (popped open), until I switched to black targets. What caused this was something in the coating that they used that made it difficult for me to resolve the outside edges of the orange dot targets. Because I couldn't accurately see where the true edge of the target was, it was difficult for me to place the reticle in the center. As soon as I changed the color, group size immediately went back to what I expected.

 

[sawgunner2001]

Tried other targets and a different optic/mount set-up, same results. New 18.5" Criterion barrel from Fulton Armory inbound. I decided to stick with .308 in the gasser. When I decide I want a 6mm or 6.5mm wonder gun, I'll do it in a bolt action and sometime down the road.

 

[precision308]

I have issues shooting good groups at distance duebto mirage. One thing thatiI've noticed that helps me is turning down the power to help lesseb the mirage