Ned Ludd
Silver $$ Contributor
G7 BC is effectively independent of velocity, remaining relatively constant over the typical velocity range we shoot. However, I believe what you're asking is at what velocity do the BC advantages of the 90s overcome (in terms of resistance to wind deflection) the performance of the 80s. Is that correct?
The typical Berger 80-something gr .224 bullet will have a G7 BC in the neighborhood of 0.227, the 90 VLD box value is 0.274. Using generic atmospheric inputs, in a full-value 10 mph wind JBM Ballistics predicts a 4.4 MOA (27.4") deflection at 600 yd for the Berger 80.5 Fullbore at 2950 fps, and 3.7 MOA (23.0") deflection for the 90 VLD at 2850 fps. Both of those are pretty reasonable velocities for tuned loads with those two particular bullets.
So there is a difference of about 4.4" in wind deflection for a full-value 10 mph wind between the two bullets at 600 yd. What this tells you is that if your ability to read the wind accurately is good to about a 3 mph difference, the effective difference in wind deflection between the two bullets at 600 yd would be about 1.5". In F-TR, that's a LOT...it's HUGE. Having shot both of these bullets, I can tell you that here is no comparison between the two in terms of wind deflection at 600 yd (or farther), the 90s will win hands down.
Obviously, wind deflection is not the sole arbiter of bullet performance. Precision, ease of tuning, cost, brass life, and other concerns are also part of the equation. In my hands, both the 90s and 80s seem to tune equally well and with very good precision, I haven't had issues tuning either one. I have had friends tell me they thought the 80.5 Fullbore, which is an outstanding design by the way, was easier to tune. So there may be differences in personal preferences and/or experiences. I suspect running the 80.5s at about 2950 fps would be easier on the brass as well. Pushing the 90s at 2850 fps out of a 30" pipe is a brass killer, maybe 3-4 firings tops in my hands. However, the performance is outstanding, so everyone must decide for themselves how much they're willing to spend in order to win in terms of competition.
The typical Berger 80-something gr .224 bullet will have a G7 BC in the neighborhood of 0.227, the 90 VLD box value is 0.274. Using generic atmospheric inputs, in a full-value 10 mph wind JBM Ballistics predicts a 4.4 MOA (27.4") deflection at 600 yd for the Berger 80.5 Fullbore at 2950 fps, and 3.7 MOA (23.0") deflection for the 90 VLD at 2850 fps. Both of those are pretty reasonable velocities for tuned loads with those two particular bullets.
So there is a difference of about 4.4" in wind deflection for a full-value 10 mph wind between the two bullets at 600 yd. What this tells you is that if your ability to read the wind accurately is good to about a 3 mph difference, the effective difference in wind deflection between the two bullets at 600 yd would be about 1.5". In F-TR, that's a LOT...it's HUGE. Having shot both of these bullets, I can tell you that here is no comparison between the two in terms of wind deflection at 600 yd (or farther), the 90s will win hands down.
Obviously, wind deflection is not the sole arbiter of bullet performance. Precision, ease of tuning, cost, brass life, and other concerns are also part of the equation. In my hands, both the 90s and 80s seem to tune equally well and with very good precision, I haven't had issues tuning either one. I have had friends tell me they thought the 80.5 Fullbore, which is an outstanding design by the way, was easier to tune. So there may be differences in personal preferences and/or experiences. I suspect running the 80.5s at about 2950 fps would be easier on the brass as well. Pushing the 90s at 2850 fps out of a 30" pipe is a brass killer, maybe 3-4 firings tops in my hands. However, the performance is outstanding, so everyone must decide for themselves how much they're willing to spend in order to win in terms of competition.