[LouBoyd]

Perhaps my chart was somewhat (or a lot) misleading. i was not trying to say that by using high BC bullets it becomes practical to shoot subsonic at ranges of 1500 yards. In most cases the practical range for a subsonic bullet is limited by vertical stringing. This is because vertical drop is exactly proportional to the >square< of the time of flight. I only posted the chart to show the effect of BC on delivered energy.

Here's a more realistic comparison. Assume two 458 caliber bullets, one with G1 BC in the 1000 to 800 fps range of 0.4 (cast lead Postell?) and the other with a BC of 0.8 (copper alloy VLD). Assume they're both 500 grain. Assume you can load them both for for a 1% extreme velocity spread (995-1005 fps) and assume you can estimate average cross wind velocity within 2 mph. What group size should you expect vs range?

Parameter 0.00 200 400 600 800 1000 range to target in yards (for all below)

Velocity drop resulting from atmospheric drag
.4 velocity 1000 915 849 793 744 600 feet/sec
.8 velocity 1000 986 976 915 849 820 feet/sec

Energy (1/2 MV^2)
.4 energy-- 1100 930 800 698 614 542 ft-lb
.8 energy-- 1100 1011930 861 800 747 ft-lb

Angular vertical drop relative to bore sight
.4 vertical 0.00 17.3 56.3 99.8 148 200 MOA
.8 vertical 0.00 16.5 52.6 90.7 131 174 MOA

Horizontal group sizes in inches from wind deflection
.4 wind d 0.00 1.0 3.9 8.5 14.9 23.1 inches for 2 mph estimation error
.8 wind d 0.00 0.5 2.0 4.4 7.7 11.9 inches for 2 mph estimation error

Vertical group sizes in inches from velocity dispersion
.4 stringing 0.00 1.4 5.5 12.0 422.4. 34.5 inches for 10 fps mv variation
.8 stringing 0.00 1.5 5.4 12.1 22.2 33.8 inches for 10 fps mv variation.


Conclusions:
Doubling the bullet's BC from .4 to .8 has the following effects:

1. It results in a moderate increase in delivered energy.

2. It educes overall drop but only by a small amount. Drop at ranges in excess of 600 yards requires specialized scopes with very large vertical adjustment range for either bullet. (A Leupold Mk 4 16x40 will barely make 800 yards with a .8 BC bullet).

3. Wind deflection is reduced close to inversely with BC. This is the most important reason to use high BC bullets.

4. BC has negligible effect on vertical stringing at least between .4 and .8 BC. Note that the effect favors high or low BC bullets at different distances. This is the result of the shape of the G1 drag model which is not a smooth function as normally implemented in ballistics programs. It isn't easy to handload subsonic ammo 1% extreme spread (10 fps) but it can be done.

How far you can shoot with subsonics becomes a matter of:
1. how large of group size is acceptable for your application?
2. how well can you measure or estimate the effect of crosswinds?
3. how small of velocity dispersion can you achieve with your loads?
4. How much energy do you need at the target?

I'm showing no error for distance measurement or atmospheric density since both can be directly measured accurately. Nor for aiming or rifle quality. Those should be negligible