Originally Posted by britz
well, I've been busy as heck this year and haven't gotten out shooting much, but I did yesterday again. I was shooting my savage 12 w/ a 12 twist 22-250 and 40 gr vmax's set on top of 39.5g IMR 4895. I was getting about 4250 fps w/ my chrono ( not sure how accurate it is but I think it is in the ballpark???). <snip>
I've had much better luck with the 40g NBT and 55g NBT in my Savage LRPV than with V-Max bullets. The results you are getting are pretty ragged, more ragged than I'd expect to see from just a bullet difference.
Things that come to mind as making a rifle erratic like that are:
Loose scope mounts.
Bad bedding/loose action screws.
Barrel touching the stock someplace.
Loose barrel/receiver joint (not torqued enough).
Bullets inconsistantly touching/not touching the lands.
Brass that's right on the edge of being too long so some crimps bullets, some doesn't.
Reamer chatter in the chamber and throat.
Damaged crown (if there is an abberation on edge of the the crown, no matter how small, if it is big enough that you can see it, it's a defect that can cause problems).
Goobers in the barrel. Bore sighter damage near the muzzle, cleaning rod damage on either end, <whatever>. I just looked at a .22-250 that had a whole land worn away on one side of the bore at and beyond the throat from cleaning rod damage (the guy doesn't believe in bore guides so he gets to buy a new barrel).
Bore exhibiting severe tooling chatter (makes them copper up real fast).
Thermal errosion in the throat.
Severe eccentricity in loaded ammo.
Action severly out of true.
Bolt mating with only one lug.
Loose bolt with lots of vertical bolt play back near the bolt handle.
You might learn a lot from a good borescope examination. I've seen some pretty amazing things in rifles with "new" barrels.
First thing I'd do is check the easy stuff first. But I'd check for all of it. It has to be "something". And there is no rule that says it has to be just one thing. It could be several things wrong.