however, if you hang around the reloading forums, or people who own chronographs, you'll find that
1) 20 different rounds from the same lot of ammo may have more than 100 fps difference between the fastest and slowest measured
2) the average speed (constant ammo) through individual barrels of the same length may vary by 100 fps due to differences in chambers, rifling, lining, etc
i mostly just work on trigger control these days