I have a fascination with the odd and esoteric wild cats but from a practical point it is best to keep it simple.

One case that I keep thinking about is the 7 x 65R case. By using this case and a 280AI reamer you would end up with a 7 x 65R AI a rimmed 280 Improved. The same thing could be done in 6.5 mm. By using two reamers or a custom neck/throat reamer you could avoid the cost of a full custom reamer. The rimmed case is only an advantage in break open doubles, singles and falling block single shots with less extraction power than the Ruger #1.

For the #1 you couldn't go wrong with the 6.5/06 Improved. The 6.5 long Krag improved would be a rimmed option but more involved case forming. The 6.5 x 284 might be trickier to get positive extraction but the reamers and dies are readily available, as are cases. The 6.5 Rem Mag is no slouch in a 26 inch barreled rifle, but it is almost obsolete itself.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli