The only way to find out is to shoot at 100 yards, that's the only technique I've found to be truly reliable. If that doesn't work, sighting in to zero at 50 yards should put you about three inches low at 100 yards. By the way, the muzzle velocity is probably closer to 1600 or 1700fps from a Contender barrel. My 240 grain loads in a 10" barrel are right at 1600fps. The same load from a 6.5" revolver barrel goes 1350fps.