Re-barreling won't be the problem, the gas port will. I don't know anyone who would do this although I've read of it's being done. I would bet the price would be truly amazing. The 760 in 35 Rem to 358 Win is easy, it's just a rechamber and in a pump even, nothing else need change. The gas operated Browning would present a lot of problems.. You must balance the energy needed to operate the mechanism and to overcome the return spring with the load and the size of the gas port. Good luck!