I know this is an old thread, but it was very helpful to me and I thought I would add my experience to perhaps help others. I just got finished converting my german Mauser 98 to 450 BM and as others suggested it is indeed a very doable project. The action was a barreled action in 257 roberts I picked up years ago on gunbroker. A new bolt handle had been welded on as well as a nice latched floorplate conversion, but other than that the entire barreled action was in rough shape, but some TLC and rust bluing fixed that. I inletted the entire thing into a custom walnut blank myself, it was my first time doing this and while its not 100% I learned a lot and its something I am very proud of. It would never shoot well and ended up spending most of its life in my safe until I started research the 450BM conversion and found this thread (and others). I ordered a 450 barrel blank from X-Caliber and had my gunsmith thread and install it. This was then re-inletted into the walnut stock. It turns out that the magazine box was binding a little on the action and this was perhaps why the 257R never shot well, but that was corrected this time around. I wasn't lucky at all when it came to getting the cartridges to feed from the magazine. As is, they wanted to nose dive in the magazine box and if I nudged them up with my finger they would end up binding in between the feed rails and not popping up on top. I tried the detachable magazine FSJeeper suggested. Initially it wouldn't fit into my magazine box, after a little modification it would but feeding was gritty at best and controlled round feeding was hit or miss. Plus, I would have to do away with my latched floorplate. After I little tinkering I found that if I used a short-action follower and spring from my 1990's era Rem 700 and loaded the cartridges towards the back of the magazine well (but not all the way back) they would start to feed well but hung up a little at the 98 feed ramp. I purchased a new production Rem 700 spring and follower from a member on here, trimmed about 1/4 inch off the front of it with a dremel, and installed it towards the back of the magazine box. At the front of the magazine box I fitted a UHM plastic block as a spacer, the top of his block I tapered with a rasp so that it acted as a pre-feed ramp of sorts. Cartridges fed perfect after this, except for the very last cartridge which I needed to place a bead of JB weld on the follower to move that cartridge a little more to the center of the magazine well and then it fed. I didn't have this problem with the 1990's follower, just the new production follower which was shaped a little different. This is my second X-caliber barrel, both are very accurate and I am looking forward to testing this one in deer gun season.
