69 grain HPBT, BC .301:
adjustments:
100 yards 1.00 MOA
200 yards 2.25 MOA
300 yards 3.50 MOA
500 yards 6.75 MOA
600 yards 8.50 MOA
1000 yards 16.75 MOA
77 grain HPBT BC .372
adjustments:
100 yards .75 MOA
200 yards 1.75 MOA
300 yards 2.75 MOA
500 yards 5.00 MOA
600 yards 6.50 MOA
1000 yards 12.75 MOA
Thanks.
The above confirms that my one and only miss last weekend (1.25 inches outside the 5 ring @ 500 yards, or a miss from the center of the X by about 19 inches) would have been a 6 or 7 ring hit had I sent the same shot with 77gr ammo rather than 69gr ammo.
(shot with 69gr, bullet moves 6.75 MOA @ 10mph crosswind @ 500 yards = 33.75 inches, while a 77gr move 5 MOA @ 10mph crosswind at 500 yards = 25 inches... 8.75 inches inwards on the target. The wind only switched on the last half of the distance down range and I was dialed 5MOA "in" to the wind as I read it. So I moved 2.5MOA into the wind correctly, but about 3.5MOA in the wrong direction due to the wind switch, resulting in being 3.5 MOA off... half the scoring bull, just outside the 5 ring. Had I been shooting 77's, I would have dialed 5 MOA into the wind, had correct windage for 2.5 of that and incorrect windage for the other 2.5, putting me 2.5 MOA off center. That's a 7 or 8 ring hit.
69gr:
X---10---9---8---7---6---5-x
77gr would have been here:
X---10---9---8--x7---6---5
Target = 7MOA with white 5 ring, about 36 inches across. Moving inwards 8.75 inches puts me at (37.25 inches - 8.75 inches) 28.25 inches from center. That's on the outer edge of the 6 ring just on the edge of the black. I had a R-L 10mph crosswind that completely reversed on me halfway downrange as I was getting into position and I didn't see it until I broke cheek weld after the shot had already gone down range. I knew I had basically shot with the wind helping to push me the last half of the distance off target. Heavier bullets would mean less windage dialed in the first place, along with less negative affect from an erroneous or missed wind call. Alas, stuck on 69's until my White Oak arrives...)
Interestingly:
Your data for 77gr:
100 yards .75 MOA
200 yards 1.75 MOA
300 yards 2.75 MOA
500 yards 5.00 MOA
600 yards 6.50 MOA
1000 yards 12.75 MOA
Using the Hoffman formula, I come up with:
100 = 1(for hundreds of yards) x 1 (for 10mph wind) x 1 (for full value wind) = 1 MOA
200 = 2 x 1 x 1 = 2 MOA
300 = 3 x 1 x 1 = 3 MOA
500 = 5 x 1 x 1 = 5 MOA
600 = 5 x 1 x 1 = 6 MOA
1000 = 10 x 1 x 1 = 10 MOA
Doesn't seem to be insufficient until out to 600 yards, and starts to lose its accuracy significantly at 1000. At least for 77gr.
It appears that at 500 yards, though, Hoffman isn't gonna cut it for 69gr ammo. Compare the Hoffman above, to your data:
69 grain HPBT, BC .301:
adjustments:
100 yards 1.00 MOA
200 yards 2.25 MOA
300 yards 3.50 MOA
500 yards 6.75 MOA
600 yards 8.50 MOA
1000 yards 16.75 MOA
It's off by 1.75 MOA (almost 1/3 of the target) at 500, and 2.5MOA at 600 (nearly half).
If I augment Hoffman and change my fundamental assumption of holdoff for 10mph wind when using 69's... I guess I'd use distance + 33%, then 1 MOA per 100 yards of that calc'ed distance for a 10mph full value wind.
100 = 1.33 * 1 * 1 = 1.25 (off by 0.25)
200 = 2.66 * 1 * 1 = 2.5 (off by 0.25)
300 = 4 * 1 * 1 = 4 (off by 0.5)
500 = 6.67 * 1 * 1 = 6.5 (off by 0.25)
600 = 8 * 1 * 1 = 8 (off by 0.5)
Or, stating it differently... add 1/3 more windage than I'd use if I were using a 77gr bullet, or 147gr .308. At least for the 500 and 600 yard targets. The effect of wind increases at longer distance, and adding 33% to 100/200/300 yard targets introduces error.
I had always just assumed about a 10% difference in windage efficiency between 69gr and 77gr bullets. I had no idea it was as extreme as your data shows. Thanks, Dick. I'll spitball with 69gr, adding 33% to my current windage numbers.
