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DOPE question - how can .22LR be lower at 30 & 50 yards than it is at 25 yards?

Sheriff_Will_Teasle

Private
Minuteman
May 12, 2020
34
21
Front Range CO
Hi all -

In working out my dope on a suppressed V22 with scope height of 2.38", I encountered something odd. All ballistics calculators show that with a 25 yard zero you should expect to be about 2 clicks high at 30 yards. I got 2 clicks low at 30 yards, so that's a 4 click differential. The differential is still 2 clicks at 50, 1 click at 100, and then no difference between calculators and my data out to 230 yards. Also note that I took the suppressor off and all data was the exact same.

My question is, do I believe my DOPE or is it impossible to shoot lower at 30 yards with a 25 yard zero, 1061 FPS, DA of 8000, temp of 88F and scope height of 2.4"?

As I try to answer this question with math, my first thought is to calculate the gravity induced drop from 25 to 30 yards using d = 1/2at^2 and see how that compares to the drop from 2 clicks worth of angle (if 2 clicks is a bigger, then I know it is impossible).

Time of flight from 25 to 30 yards is 20 msec with an average velocity of 1025 FPS
Drop due to gravity is thus = .08"
One mil of angle at 25 yards is .075", so 2 clicks would be .015". Since 2 clicks is so much smaller than the gravity drop, I think that this is possible to explain my DOPE with barrel harmonics.

Does anyone else have any .22 DOPE that shows 30 yards lower than 25 yards?
 
I zero at 50. I'm within .1 at 25, but I am .2-.3 high at 33-35 yards with a 1.8" height over bore and a 20moa base.

You're probably on the down slope already. See how far off you are at 50.

Then try zeroing at 50 and see how far off you are at 25, 30, 35, 40.

Them you'll see why the zeroing at 25 or 50 argument is silly.
 
Yes, it happens. Just true your data and move on.

Especially if you’re shooting prs/Nrl. This isn’t going to be what costs you a match.