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POI Variance

14 Feb 2019
@ 02:53 pm (GMT)

Luis Vazquez

Hello 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. 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

Luis


Replies

1
14 Feb 2019
@ 05:37 pm (GMT)

Vince

Re: POI Variance
Hi Luis,
I don't have an explanation but have had a similar experience with the same cartridge. I originally used Hornady American Whitetail 139 gr factory ammo in my Ruger American, then switched to handloads with the 150 gr ELD-X which had a very similar poi (less than an inch) from the 139's.
Recently on Nathans recommendation I swapped to the 162 grain ELD-M in handloads which shoots to basically the same elevation but 4 inches to the right of the other 2 rounds. It is very consistent averaging around 0.7 at 100 yards so no complaints and is 1 for 1 on deer to date, interesting though that you went down in weight while I went up but we both headed right!
Cheers
Vince
14 Feb 2019
@ 09:44 pm (GMT)

Thomas Kitchen

Re: POI Variance
HI Luis
I might be wrong but I think it mainly relates to the spin
the light projectiles have a higher velocity so have higher rpm.
This video is really good for visualizing it https://youtu.be/mhGp2bAdYXQ

Now assuming you run a light and heavier projectile at same velocity will the change be as much? and would your change of poi be more based on harmonics
oh no off down the rabbit hole we shall go.
15 Feb 2019
@ 06:40 am (GMT)

Luis Vazquez

Re: POI Variance
Thanks guys for your replies. That is strange Vince, they provably go right due to the spin of the bullet and like Thomas mentioned provably barrel harmoics as well.

Cool video Thomas, spin definitely does have an effect, same goes when playing tennis or baseball

Thanks again and best regards

Luis
15 Feb 2019
@ 08:05 am (GMT)

Frank Vallich

Re: POI Variance
Firing a .308, 1 in 12 twist, 4 lands and a 26 inch barrel at 100 yards the following observations.
BARNES 168, dead center.
HORNADY Z MAX 168, 2 Inches high dead center.
HORNADY ELD X 178, 5 Inches high and 2 inches right of center.
This is allowing 5 minutes between shots at -5C.
Consistently this occurred on the two separate days.

The accuracy of the ELD X was superior to either 168.
The velocity and force best the 168s. Will probably use the 178 as my all round hunting cartridge and use 168s for the open site R1 .308.
Surprisingly laughable when I target an 8.5 X 11 inch target with the open sites as the paper almost disappears at 100 yards. Still close to vertical center but typically an inch or two low.
16 Feb 2019
@ 10:51 am (GMT)

Warwick Marflitt

Re: POI Variance
Well I guess you just have to write down the different loads turret settings so you can switch loads adjust clicks and go.
16 Feb 2019
@ 11:00 am (GMT)

Frank Vallich

Re: POI Variance
Will dial in the 178 ELD X for 500 zero as my all round cartridge. No time for swapping mags and dialing knobs in sub zero temperatures. The 168s will be used in the Benelli R1 open sights for 100 yard ungulates and bear deterrent.
16 Feb 2019
@ 11:38 am (GMT)

Luis Vazquez

Re: POI Variance
Quote:
Well I guess you just have to write down the different loads turret settings so you can switch loads adjust clicks and go.


Not a bad idea, although I usually check my Ago before every hunt or at least once a month when I go to the range. But to your point its not a bad idea, you can switch from deer load to a coyote one im with justva few clicks and done. Thanks for the input

Luis
16 Feb 2019
@ 11:38 am (GMT)

Luis Vazquez

Re: POI Variance
Sorry, I meant check my zero
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