I too have a S&W Mountain gun in .45 colt. I don't know about the 335gr. load, but my load for max thump is a .300 gr. LFNGC w/ 24grs of W296. Either load will do, the point is, "carry much and shoot little" with this load. Sight in your gun for your thumper, but practice/plink with a lighter load so as not to over stress the gun.