Sometimes the factory data is right on the money in some guns. Most of the times they are not. For example, my 460Smith&wesson with 200gr factory ammo is dead on the specs by hornady at 2200fps. But, one I have a very tight bore, and its a Perfromance model, with a 10.5" barrel. Ihave 3 friends with the X frameregular smith model with thegain twist barrel,and all 8" barrels, and none can come 150fps to the claimedHornady velocity. Does that mean hornady's claim is false? No,not exactly.

It has alotto do on how thechamber is setup, howmuch freebore, and how loose the rifling is.And of course barrel length.