Unless your barrel's got the same chamber, bore and groove dimensions as the one the load recipe was developed with, your muzzle velocity can easily be 50 fps faster or slower than the data claims.
And your powder and primer lots are not the same as what the load was developed with. This will often change chrono'd loads 25 fps different than what the manual says.
Even with two people shooting the same rifle and ammo, a 25 to 50 fps difference in average muzzle velocity happens a lot 'cause the rifle's not held the same way by each shooter.
It's rare that anyone duplicating a published load gets the same muzzle velocity quoted for it. Even allowing for a 25 fps change for each inch of barrel length difference.
Originally Posted by Broz
Working out drops to 1000 yards will give a better idea of real velocity. The proof is in the pudding.
It's possible, but how does one compensate for the inaccuracies of virtually all scope adjustment values per click? All internally adjusted scopes of a given make and model do not have exactly the same amount of impact change per click. To say nothing about the atmospheric conditions between the rifle and target that'll change the bullet's drop and there's no way you can measure them when the bullet's fired.