Horizontal POI shift with specific load in a gas gun

[CM^2]

Experiencing a somewhat odd POI shift in my Krieger barrelled Ar-10. This weekend I experimented with Prime 130's in it for the first time and recorded a repeatable .5 mil windage shift over established zeros for all the other loads. My first reaction was to go through the nut/bolt checklist to make sure nothing shot loose but everything checked out. I've never had a POI shift horizontally in a bolt gun like this. I'm new to the autoloader platform and wondering if it's unique to the gas gun.

I have historically shot 120 Amax, 123 Copper Creek Amax, 140 Hornady Amax and ELD all with predictable and repeatable elevation changes.

suppose my question is, "does a half mil windage change seem unusual? does it deserve more inspection, or shall i just log it in the data book and keep shooting?" interested in other experiences.

thanks

 

[Citius7]

Is it heat in your barrel? I've had the same issue in our 260 R.E.M. Shoot it cold and watch it walk. Then let it cool.

 

[CM^2]

doesn't seem to be...the control groups before and after with the baseline ammo went to same spot.

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[Citius7]

Hmm. Gas guns are def a funny thing. I know this sounds crazy simple and not an insult.... all ur screws tightened on ur scope and base? What about pressure on the bipod? Sometimes when you allow gas guns relax in ur firing position that play between the upper and lower fit could have a different outcome. Follow through like a robot? Sry for simplicity.

 

[CM^2]

yah. my first move was to but and bolt the entire package. found nothing amiss. Shots were from sandbag rest not a bipod.

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[tnichols]

Half a mil is a far amount, BUT, if it's accurate and consistent, log, make the necessary scope adjustment and enjoy. Big gassers are fussier than bolts in my experience.

 

[BoltRunner]

Below is a question I put in the forum recently, are you running a crush washer or shim? Alot of guys seem to think that when you get some heat in your barrel with a shim or crush washer POI change can happen pretty easily due to preloaded torque and harmonic change in the barrel. Does it return to zero after cooling?

So I had heard from some benchrest shooters that on a long range PRS or Benchrest setup that you should never run a crush washer or shim with a brake. They basically said that your putting preloaded torque on the barrel and when it heats up your POI will change. They stated that on a precision rifle that was gonna shoot over 600yds it should be brake timed directly to barrel, an AR type setup different deal as that's not a precision rifle in there mind looking for one hole groups. All my brakes are seamless done by a gunsmith so besides an AR I don't mess with crush washer timing much. I've never personally heard this so I wanted to get some other opinions, anyone that shoots 1,000 an over bolt action PRS or Benchrest seen any deviation on POI from something as small as a crush washer?