A friend gave me around 60 new, unfired RP 257 Roberts cases. They are probably at least 25 years old. Since +P 257 Rob cases are kind of expensive these days, I was planning on using these standard velocity cases in my Kimber Montana. Are the standard cases made from thinner brass, so I should I work up standard velocity loads for them? Or... is it just that the head stamp is different to prevent someone from inadvertently shooting +P loads in a vintage rifle?
