Straight from Berrys website...
FAQ: How fast can I shoot these bullets?
Velocities depend on the caliber, but as a rule of thumb, we recommend you don't shoot our plated bullets over 1250 feet-per-second. Our 44's actually shoot best around 1150 fps. 45's are generally good at 850-900 fps. Our bullets are not recommended for magnum velocities over 1250fps unless the bullet description denotes a thick plated bullet with a higher listed maximum for velocity.
The recommendation is that you shoot their .452 bullets at 850-900fps not that if you exceed it you will have problems.