257 Roberts vs. 257 Roberts+P

[Bucksnort1]

I'm helping a friend with advice and by donating loading components and equipment so he can begin loading for 257 Roberts.

After searching my loading manuals for recipes for his bullet weights, I come across 257 Roberts +P recipes. I know there are handguns that shoot +P cartridges so I know these are more powerful but this is the first time I have seen a rifle cartridge in +P.

I am curious about a rifle cartridge in +P. Do you need special cases for these?

I'm sure someone will provide some history.

 

[Unclenick]

If you look at the SAAMI standard, you will find the +P version of the cartridge has 10% higher pressure than the original load. However, when you scroll down to proof pressures, you find, just as with 38 Special, the original proof load has been declared obsolete and the +P proof load is used for all .257 Roberts chambers. This means any gun that is up to modern standards will handle both. And with +P being the only proof load level, there is no need for separately stamped +P case heads to prevent accidental chambering in a gun that is not rated for +P, as they all are so-rated at this point in time. You may get a somewhat shorter case life from the +P loading, but otherwise, no issues.