I have one of these, done by a Pennsylvania gunsmith named J.W. Van Patten. There isn't a lot of reloading data out there using modern powders, but you can use .22-250 starter loads as a beginning point and work up carefully. In my experience, you can expect 50-100 fps difference between the .219 Improved and the .22-250. Perhaps a bit less if your barrel is longer than 24 inches (mine is 27).
I hope it came with brass, because it's a pain in the butt to reform .30-30 cases, which also need to be shortened a bit. .25-35 cases work fine for the basic .219 Zipper, but I've had no luck with blowing them out, even after annealing. I don't know what the difference is between the .25-35 brass and the .30-30 brass, but the latter works while the former doesn't.
