Actualy this is NOT a good idea. The problem is that these .45 rifle cases are not STRAIGHT cases, like the pistol rounds mentioned, but have a fairly pronounced taper. Thus not only do you have freebore, but a progressive widening of the chamber rearward. While the round would go down the barrel, you would have a great deal of blowby, and possibly split cases in the longer chambers. This would lead to rapid fouling of the action, interfering with rapid fire. No knowledegable rifleman would do it. The base diameter is the same, but the shorter the cartridge, the steeper the taper.
Here's another thing: the Rolling Block was never chambered for that round. Unless you reshape the breech block you can't chamber anything that long. Thus the Rolling Block in the higher capacity chamberings used bottleneck cartridges.
I realize this is fantasy, but its something to consider. Just my humble opinion, nothing more.