Re: 308 at 1000
Heavier bullets generally have the least wind drift, even though you cannot launch them as fast. I know there is a feeling that the one place this breaks down is when comparing the Lapua 155. The thought is that this bullet has a BC higher than the Sierra 175 MK, and is also lighter so you can push it faster - making it perform better at longer ranges. It seems like an excellent bullet for when you have to use a 155, but it does not seem to have less wind drift at long range than a 175 MK and certainly not a 220 or 240 MK.
The problem is that the 'advertised' BC is only for velocities above 3000 fps - where the bullet spends little to no time in flight. If you launch the bullet at 2860 and it is 1380 at 1000 yards, the average velocity is 2120. The true average BC of this bullet is about 0.465.
The SMK 175 has a higher (actual, not advertised) BC than the Lapua 155 at any specific velocity according to real-world testing.
At 1000 yards with a 24 inch barrel, this is what I compute for equal chamber pressure:
Bullet, fpe at 1000, wind drift inches (10mph), drop in inches.
Sierra 240 893 78.2 500.4
Sierra 220 793 84.6 477.2
Sierra 175 604 96.1 416.4
Lapua 155. 518 98.5 386.7
So if the goal is the least wind, then use the Sierra 240 or 220 (which would want a 1:8 twist).
The Sierra 240 has 43 MOA drop at 1000 yards if you zero at 100 yards, but if you have a 20 MOA base, that is only 23 MOA on your scope.
Here is the data for a Sierra 142 (.260) launched at the same pressure from a 24 inch barrel at 2764 fps:
Sierra 142 629 76.7 362.5
It outperforms the Sierra 240 for wind (by a hair) and the Lapua 155 for drop. It crushes .308 by combining the two extremes of long-range .308 bullet performance - and has less recoil.
But, .308 with a 1:8 twist can match it for wind! .308 shooters should switch to 1:8 twist and 220, 230, or 240 grain bullets on a mass exodus.
