velocity question

[FTRinTexas]

Friend was at the range today with his .338 lapua. Got it sighted in at 100 yards. Cranked the scope up 12 moa and was hitting 13.5" high at 100 yards.
Bullet was 250g Sierra HPBT.
Range is at 580 feet above sea level and 80 degrees, 80% humity
How do you convert this information to muzzle velocity.

 

[Doug Beach]

You don't. All you have learned is that 1 "MOA" on the scope is worth just over 1 MOA on the target. If you zero at 100 yards, and then measure your drop at longer ranges, you can roughly approximate your muzzle velocity.

 

[Zero333]

You need to know the exact BC of the bullet, shoot it at 800 yards and correlate that data into velocity by playing with different velocities in the bal. calc... 400 yards is not enough because it will give you a 50fps window at that distance with that load if your rifle is shooting 1/2moa.

But even then, you have a problem with the scope where it doesn't match actual dialed elevation, or your buddy pulled the shot when he dialed 12moa making it go 1.5" higher than it should of. Or you were shooting closer to 90 yards instead of 100yards. Verify the actual distance you were shooting with a rangefinder, don't trust yardage markings.