Discussion Forums

Bill

Hi;

I recently picked up a new .308 rifle, and while trying different factory loads I noticed that one of selections consistently drifted to the left. This doesn't make a lot of sense to me, and I was hoping someone here could point me in the right direction (no pun...)

Rifle is a new Winchester Model 70, 22" stainless barrel with a 1:12 RH twist. Distance was 100m, shot from a bench. Scoped with a 4-12x40 Bushnell. Target is one of my personal design with a small 1.25" aiming diamond to allow for as precise a shot as possible - I'm not aiming 'somewhere' within a 4" bull. The outing was primarily to confirm rifle function, try some different ammo and dial in the scope. The scope will be replaced with something better: nothing wrong with the optic, it's just one I've never really liked but was what I had on hand.

As to be expected, group sizes varied with the different brands and projectile weights, however all were more or less centred around the aiming point. Lighter projectiles impacted a bit higher than the heavier ones. All normal.

The only thing that didn't compute was that the Winchester 180gr PowerPoint group was a good 2-3" left of point of aim.

I don't believe that this was a wind issue, as winds were light, distance was not that far - only 100m - and the range has tall trees on one side and a berm on the other. So, pretty well shielded from wind.

I also don't think that this was a heat issue, as this certainly wasn't a rapid fire session, and grouping returned to centre with different ammunition immediately afterwards. I can understand a vertical string/oval, but can't figure out why the entire group moves left.

I'm aware that Winchester PowerPoint is probably not at the top of anyone's best-of list, and 180gr is perhaps just beyond what's optimum for a 1:12 twist. It is however cheap and plentiful around here, so it's what I seem to have the most of. I don't need it to work, as I'll find and buy what does. It's just been a real head-scratcher as to why it shoots left.

Most of what I've been able to find on the Internet about hits landing left seems to be oriented toward finger placement on handguns. The little bit on spin drift that I've read would indicate that it's all but imperceptible at such a short range.

Any ideas?

Thanks,

Bill