My advise is, no matter who made the gun, measure it.
Make sure your bullets will slip through the cylinder throats easily and all rounds will chamber properly. However, many cylinder throats are tapered at the origin enough that a larger bullet will chamber freely, in which case the larger size should be used. However, to be sure some rounds won't hold the ctg rims off the cylinder, seat a trial load with the oversize bullet out about 1/32 inch. If the rims drop against the cylinder in every hole, load with the bullet seated to crimp in the groove and you'll get good safe results.
Never seat heavy revolver loads where the bullets cannot be crimped in a groove. Bullets can pull and hang up the cylinder. In other words don't adjust seating depth outside the crimp for HEAVY loads but seat them deeper if you wish to make them chamber easily if the load is light enough that bullet pull from recoil doesn't move the bullets. Seating deep can make VERY pleasant light loads, and the deep seated rounds will be easily identified from heavy loads. Pressures will go up with any given load, and dramatically if bullets are seated a lot deeper, and jump to the rifling will be long and far more severe than if seated out, but if accuracy is good, the muzzle blast will be considerable less than when seated out.
Since the fellow you bought the gun from isn't a re-loader he quite possibly his 451 bullet size advise will probably not be as accurate as measuring the gun. Especially after 12 years of use. Cylinder throats do wear a little from powder erosion, but the barrel forcing cone gets 5 or 6 times as much wear, depending on how many holes the cylinder has.
