If i'm not mistakin, I believe the 351 SLR aka 351 WSL was a winchester made caliber originally came out in the year 1907 and production stopped in I think 1960
SLR stands for Self loader rifle or self loading rifle something of that sort hang on to them may have collector value. I know of a rifle the winchester Mod 07 shot that caliber. But I dont know of any other guns that were chambered for it.