Okay, just for giggles, I went and grabbed a couple things out of the gun room: a loaded round of .458 Winchester Magnum ammo and my XP-100, chambered in .221 Fireball. As you can see, it's longer than the action opening, but it funnelled in there pretty easily. With the bullet's ogive resting up against the itty-bitty chamber opening and the rest of the overlength in the locking lug area, there's maybe 1/4" of space left over. So it should work pretty smoothly, although getting the empties to fall out would likely require tipping it to the right and shaking it a little. Personally, were it me, I'd go for it if the price was right. I've got a bunch of moulds for .458" bullets and would plan on light loads. Down in Trapdoor Springfield .45-70 territory. I agree that the shorter length versions of the case would be the way to go for any sort of efficiency/performance and it might prove to have disappointing accuracy as-is: still, it'd be fun to play with and find out for sure.