For some reason, prior to the appearance of so-called Plus P loads, the factories have always sort of short-changed 257 Roberts owners by underloading this cartridge. I say "for some reason", because no weak-actioned rifles were ever made for this round, at least no weak commercial rifles. Maybe some custom-made jobs on M93 or 95 Mausers, but the factories don't load ammo taking such matters into consideration. The .257 Roberts is basically nothing but a Mauser 57mm case necked to shoot .25 caliber bullets, and Mauser 57mm cases are NOT WEAK! In other words, there was no need to strengthen .257 Roberts brass in order to load this round up to its' potential. (Just look at the operating pressures of the 6mm Remington, for example!!) Hence, there is no reason to suspect that .257 brass which is NOT stamped "+ P" is any weaker than that which carries such a mark.