Banen, don't think anyone explained the +P 257 ammo to you. The 257 Roberts had its beginnings as a wildcat cartridge (7 X 57 mauser necked down to 25 cal.) which eventually was produced by Remington and etc. The wildcat versions were pretty hot cartridges in their day and when Remington and the others began producing it, they reduced the powder load that no where approached the velocities achieved by the 257 wildcatters. Many years later, the + P was factory produced which had higher velocity and, of course, pressures. I have a 1891 Argentine mauser action that I had rebarreled in 257R. Great shooting rifle, but I should only shoot the regular load 257R ammo in it, which pretty much limits me to Remington ammo. Shooting the 257R +P ammo, which is what Federal, Winchester and others make, in my old small ring Argentine action would not be wise to do. Furthermore, with the development of the .243 and the 25-06, the popularity of the 257 Roberts began a serious decline, which is a shame for it is still an excellent cartridge.