It depends. Do want to actually KNOW the velocity of your loads or are you happy with the maker's published data?
Its been known to be "adjusted to favor the product" sometimes by ludicrous methods (16" test barrel for a pistol, for example).
I just worked up some new loads using unfamiliar components, the maker says the bullet powder charge combination is good for 1470 FPS. When I ran the load over my chronograph it was 1126 in the real world.
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”