I can't speak for all of them, but my 45-70 Handi shot quite well with the Lee 405 plainbase bullet up to about 1500 fps, the RCBS 405 gascheck bullet to 2000 fps and the RCBS 300 gascheck bullet up to 2200 fps. At these levels the recoil is fearsome, and not all that much fun. I tended to run it at black powder velocities or so, at which point you don't need gaschecks or hard bullets. Just plain ole wheelweights with a pinch of tin, aircooled, with some 50-50 Alox/beeswax lube works great. Just make sure your bullets are at least as big as your groove diameter and you'll be fine. Start with bullets about 400 grains or so, the lighter ones are sometimes harder to get to shoot as well.