I just checked the load data on Barnes website for the 250gr Casull. The max load they have listed is about 1500fps+ with that bullet in handgun. Although im sure it could handle much faster speeds.

The 45/70 data for a Barnes 458 250gr can exceed 2500fps in the upper end loads for strong actions. Thats pretty similar to what a Savage can do with the same bullet and even the same powder. Its possible this one is a bit tougher but ive looked at them. They looked really similar to the .452 250gr XPB, im pretty sure they would still expand at sub speeds too.

50S&W 275gr data is really close to the the 54x50 speeds a GMB54 can achieve with the MZ 275gr bullet. Ive used both and besides the cannelure, i couldn't tell a difference in the two 50-275gr bullets. Ive shot these from mild to max and not one failed to expand on media or produce a quick humane kill. Its one of my favorite bullets but the BC really sucks if you want to shoot much past 100 yards.