Poi variance


Well-Known Member
Feb 2, 2019
Tucson, Arizona
Hi All:

Today I saw something that I have never seen before while zeroing in my 7x08 for my upcoming Javelina hunt.

With this caliber I've always hunted and shot in competition with bullets weighting 139gr, 140gr, 150gr and 168gr, nothing lower.

I developed a load a few months ago for some 120gr bullets I acquired a while back and decided to use these on Javelinas and Coyotes, nothing bigger, maybe, maube coues deer. I had sighted this same rifle with 139gr SST's about a month ago and was dead on at 200 meters because I was going to hunt with this load before I decided to use the 120's.

Today when I shot the first round of the 120gr BT it hit 5 inches to the right, I fired 3 more rounds and all did the same, all 4 rounds grouped under 0.5" and all 5 inches to the right from the center of the target.

I then fired 3 rounds with the 139gr SST load and these were dead center on target, all grouped under 0.7", which is what this load usually produces. I then let the barrel cool off.

Once the barrel cooled off fired another 3 rounds of the 120gr and again they hit 5 inches to the right so I adjusted the scope and got the rifle zeroed at 200 meters.

When I shot at 100 meters is was 2" high above the center of the target as expected and was 7" low at 300 meters, on both distances it was above and below the center of the target, it did not vary to the left or right.

I have never fired different bullets weights at the same time, at least not a 20gr difference between them. Can anyone tell me why this happened? Is it the difference in bullet weight or what?

Thanks all and best regards

Barrel harmonics.
Similar, I am working up a new load with 162 amax in my 7-08. At 100yds it lands exactly 2" left of my 150gr hunting load.
I suspect it's more a matter of barrel harmonics. It's possible for many heavier, bullets to shoot higher, or the same bullet with a higher powder charge to shoot lower. It just depends on the whipping (rotating) of the barrel when the bullet leaves the muzzle. That's why a lot of us do ladder tests to develope a long range load. Hope this helps.
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