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Ammunition drifting to the left

31 Jul 2017
@ 05:43 am (GMT)



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?




31 Jul 2017
@ 07:36 am (GMT)

Chris Murphy

Re: Ammunition drifting to the left
Hi Bill hard to say without seeing you shoot or having rifle and targets in hand but I would say the win ammo is just on a different harmonic node causing different poi
31 Jul 2017
@ 08:07 pm (GMT)

Mike Davis

Re: Ammunition drifting to the left
Bill with all due respect good sir...wash thy mouth out.......
the winchester power point 180grn is a plurry AWESOME load for the .308 at bush stalking ranges
2-3" to left wouldnt faze me in know where its going to hit so could use your normal load and keep using these bad boys for bush stalking where most shots will be 50 yards or less.
I shot a velvety red stag last year good solid chest shot..he went 20 yards and the blood trail was something Ive never seen was like someone had a 4" paintbrush and tin of red said an AWESOME load.
01 Aug 2017
@ 03:52 am (GMT)

Bryan Webster

Re: Ammunition drifting to the left
From another point of view Bill, it is also possible that your barrel was only in the early stages of being broken in. At times i have seen barrels do this kind of thing and it is also possibly related to different harmonics with each load given variables like different copper alloys and pressures.

My Benchmark 7mm 5R barrel did this all with a single load I used to break it in but suddenly ended up with tiny bughole groups and I sighted it in for that load after playing with it for a bit.
01 Aug 2017
@ 12:42 pm (GMT)


Re: Ammunition drifting to the left
Thanks guys. When I get the new optic on it, I'll wring it out a little more and hopefully it'll settle down.
01 Aug 2017
@ 01:54 pm (GMT)

Jeremy Tye

Re: Ammunition drifting to the left
Hi Bill

I am going through a similar process with a new M70 but in 7mm-08, trying different factory loads at the range at 100m trying to find the optimum. Remington Corelokt 140gr is the best by far for tight groups however I guess consistent conditions using the same set up is important to accurately compare, ie I'm getting slightly different results at 2 different ranges using different rifle supports, (sandbags at one and portable shooting rest at the other). Will test 3 other loads and will stop at that but very impressed with the rifle. Great piece of kit that been around for a long time but not often seen in retail stores here.


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