The design goal of the 50 AT and the 458 AT for that matter was never as a "Stopper" rifle but for an option for a heavy tactical rifle in the class of the 50 BMG but in a much lighter rifle.
Something that offered legit +1000 yard reach, more kenetic energy then the 408 CT but in a comparible weight rifle.
The rifle design was to be around 18-19 lbs. Lehigh makes a solid high BC bullet for the 458 caliber and at the time I designed my 458 AT reamer, Wildcat Bullets was going to order bullet making dies for a 600 to 700 gr HPBT lead core bullet in .458" caliber with a BC in the .800 to .850 range.
The 50 AT was designed around the 750 gr A-Max and it can drive this bullet to within 100 fps of what the standard 50 BMG can drive this bullet to using conventional 50 BMG chamber pressures.
All that said, if loaded to more moderate levels, either could be chambered in a rifle such as the CZ magnum receiver that will accept the 505 Gibbs and use conventional big game bullets.
Yes, recoil would be far more then pleasant!!! I tested the 50 AT in a 16 lb rifle with poor muzzle brake
for the rifle design and recoil was brutal. With the new muzzle brakes
I have now in the Painkiller line, I suspect it would be much more pleasant to shoot but have yet to test that theory trying to get caught up with shipping times.