Go to the Berger Bullet Website and download their FREE ballistic program.
Input the data to the program and you'll get your answer. Like anything else, the more accurate your imputed data, the more accurate the results.
Find the BC of the bullet you're using, get the velocity. Measure the height of your sight above the bore (this is more important then people think).
If you don't have a crony, estimate the velocity using a reloading manual, use the estimate for the BC program, THEN go out and shoot it at different ranges. Using your shot groups at different ranges, (high or low compared to the point of aim) then playing with the programs velocity input until you get the same drop/rise will get you pretty close velocity wise.
Check the weather on your computer to get the environmental data needed it.
Remember, garbage in, garbage out. The more accurate the input data the more accurate the output.
I also use the Shooter Program on my Ipod. If I put in the same data as I put into Berger's program, I get the same out put from the two programs.
Forgot to add: ALWAYS check your data on the range, BC programs will get you close, actual shooting will get you closer.