fuhrmann,
If you have the rifle and chambercast "in hand", you are in a better position to know the dimensions, than I. If you believe it is a 450 base cartridge, I suggest you obtain an empty 450-400/ 3" case( currently available from Hornady, I believe), and try it in the chamber. If the caliber of the rifle is as large as described, this case should have enough taper and a small enough neck to fit into your chamber, if it is for a 450 base cartridge. If it doesn't chamber, I suggest you "smoke" the case with a candle, lighter, or magic marker, and find where the interference is. If the interference is at the base, it is not a 450 base chamber, if it is in the neck/shoulder area; either size or cut off the case, and try again. If it fits, this time, then you have a source of cases( or if you find it more economical, you might try modifying Starline 50-110 Win. cases). If it still doesn't chamber, you should relook MB cases.
Mike
