I had a very nice M-S carbine in 6.5x54 as a youth, and let it go in a weak moment. At that time, Dominion was loading for that chambering. (I know, it dates me!!) There was one choice only, a 160 grain roundnose at 2160 advertised FPS. It shot like a house afire, and killed deer like there was no tomorrow. I don't believe I ever recovered one of those 160's from a deer, such was the penetration. The only problem I can remember with it, was the difficulty that mounting a scope would have presented. The split bridge made it quite impractical. In retrospect, It was great just the way it was. Wish I still had it. If I remember correctly, the case diameter of that 6.5x54 is an odd size, slightly smaller than the '06 family of cartridges, so boltface/extractor issues might come up if trying to convert to 6.5x55, which is slightly larger than the '06 group. Personally, I would leave it alone, and set up to load for it. Regards, Eagleye.