Consider, the .500 Jeff was designed to fit into a standard length action. That means that your CZ 550 has a lot of wasted space. Additionally, because the cartridge is so short, it is really fat. That cuts into your magazine space. So would the totally useless belt on the A-Square. Alphin designed that cartridge (the twin of the .510 Wells) because at the time the .460 Wby was the biggest case he could find. Thinking logically, therefore, if you want the power of a big fifty in a bolt gun, your best choice is the Gibbs. Now if you insist on something kind of wildcatty, you can use a standard .50 barrel and call it the .510 Gibbs. There isn't any particular use for it, but you could do that. IMO all the hullabaloo about the Gibbs having too light a bullet for its diameter is ballistic fluff. Has anyone ever heard an elephant or buffalo complain?