Using Quickload, and assuming a 6" .357 barrel, there is no way using any powder (starting with Clays and going up to include slow powders such as 2400, H110, and H4227) that a 125 grain bullet can be driven beyond the 1500 -1600 ft/sec MV range (depending upon the powder used) without exceeding the SAAMI maximum chamber pressure. I believe (but do not know) that the Quickload calculations assume use of a solid unvented test barrel, not a revolver. If so, a revolver's highest MV would necessarily be somewhat less than 1500+ ft/sec before SAAMI peak chamber pressure is exceeded.

If the Armscor .357 125 grain load does produce a MV of 1,875 ft/sec from a revolver, the peak chamber pressure would have to be horrendous. Or else they are using some magical propellant that no one else has ever heard of OR firing it from a longer-barreled rifle.