Interchangability of the magnum (7mm/300Win.) blind magazine

I'm building a wildcat on what was originally a Sav.116, 7mm Rem. Magnum. It now has an chamber length of 3.588" to the ogive. The longest that I can get from the original staggered feed blind mag. box is 3.350". With these dimensions the bullet will have to jump almost 1/4" (.238"). Roy Weatherby liked to do long free bores to reduce pressure and to increase velosity. I would rather not do it that way. Will the blind mag. metal for the RUM series fit or can it be modified to fit the catchs for the original part? Are they available in staggered feed? I realize that I might have to open the bottom of the receiver to allow the longer ctg. length. Does anyone know the RUM magazine box length and/or the catch to catch distance on it? Any info. on where I can get the dimensions, the part or the RUM part # will help. Any suggestions/ideas would be greatly appreciated. I took it out and shot it at 100 yds. with the short rounds and had 2 out of 4 differant loads (5 shot groups) that cut holes that could easily be covered with a quarter and maybe a nickel but I didn't have one....My luck!! Lord only knows what it could do if I could shoot. Thank ya'll very much, Paul :laser: