freddogs -
In .257 Roberts +P the "+P" stands for a loading pressure -- it is the same cartridge as the .257 Roberts in all other respects.
When the .257 Roberts was commercialized by Remington in 1934, it was given a maximum pressure of 45,000 CUP. The "+P" loads go to 50,000 CUP.
In my opinion, there is no reason not to go to 52,000 CUP in a modern rifle like a Ruger -- the problem is there are no factory loads at that pressure and the handloader is hard pressed to accurately determine pressure. Since I got my Ruger earlier this year I have worked up loads based primarily on data from Barnes, Hodgdon and Hornady and have been very impressed with the results. Currently I push the Hornady 75g VMAX at 3606gps with H4895 and the Barnes 115g TSX at 2958fps with H4831SC and 3013fps with H4350. While these are close to top +P loads, I do not believe they are over the 50,000 CUP mark. They are, however, incredibly accurate given that the rifle has a 22" sporter barrel.
The .257 Roberts with +P loads has proven itself to be a wonderful cartridge for my needs. For now I am satisfied shooting the centers out of clay pigeons at 200 yards, prairie dogs when I can find them, and using it as a backup coyote rifle. (Actually, it has become my primary coyote rifle - and will remain so until I get a shot at one.) This fall I hope to hunt antelope with it, and possibly mule deer. I am also looking forward to taking it 4 hours down the road to the NRA's Whittington Center where it will be used to plink the steel rams at 500 meters - something they do not allow with my 7mm Rem Mag.
Before getting the .257 Roberts I was considering getting a .25-06, which was only available in a longer action with a longer barrel. HAd I gone that route would have missed a sweet gun. Recoil is minimal (12 foot-pounds) even with my heavier 115g hunting load, and the short action/short barrel makes it a dream to handle. In return I gave up 100fps max for most loads.
Don't know why yuo are asking, but if you are considering one, I highly recommend them! (I don't think you can go wrong with a .25-06, either.)
