View Single Post
Old November 24, 2012, 08:46 AM   #12
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 5,472
Here's an excellent source on .22 rimfire bullet's ballistics:

http://www.exteriorballistics.com/eb.../22rimfire.cfm

A given bullet will have different BC's for different speeds through the air. Note the three BC's for a given rimfire bullet; one for each velocity range. To get near perfect wind drift, you'll need software that uses several velocity bands' BC values. Sierra Bullets' software may be the only one that does. Berger's software does not. If you check out Sierra's web site for their .224 dia. 90 gr. HPBT Match KIng and you'll see 5 BC's for 5 velocity bands:

.504 @2200 fps and above
.511 between 1900 and 2200 fps
.500 between 1750 and 1900 fps
.467 between 1575 and 1750 fps
.400 between 1375 and 1575 fps

The only way to get exact BC's for bullets is to measure their time of flight over a short distance at different average velocities for that distance, then compare those numbers to a standard bullet shape. Calculations based on shape, weight and speed are only approximate and sometimes way off.

And the wind isn't perfectly uniform in speed from the ground up. If the wind's 10 mph at 10 feet above ground, it could be 6 to 8 mph 1 foot above ground depending on the terrain and obstructions nearby. Ballistic software typically doesn't account for this; they use the same wind speed for bullets' path even it its trajectory's high point is 13 feet above the line of sight at 600 yards for a 1000 yard target.

Last edited by Bart B.; November 24, 2012 at 09:09 AM.
Bart B. is online now  
 
Page generated in 0.04678 seconds with 7 queries