Because your gun is .357 Magnum, you are not limited to .38 Special pressure levels in the .38 Special brass. You can safely load the .38 Special cases to 35,000 psi. The pressure rating is for the gun, not the cartridge. The problem is you cannot simply use .357 Magnum load data to do this because it will be overpressure in the shorter cases. But you can safely exceed .38 Special +P load data in that gun, which is actually a particularly strong .357 Magnum that uses a very large diameter cylinder for only 6 .357" chambers. The cylinder walls are very stout. Still, I am only suggesting exceeding .38 Spc +P pressures, not exceeding .357 Magnum pressures. I do not recommend doing this with fast powders like HP-38, Titegroup, or Bullseye. The pressure goes up too fast. Instead, use slower powders and work up. You can be sure that the .357 Magnum maximum loads will be too much, so you'd want to stay well below them. This practice is not unprecedented at all. Prior to the creation of the .357 Magnum, people like Elmer Keith and numerous others loaded strong S&W N-frame .38 Special revolvers to more than 40,000psi. S&W sold revolvers for this practice and factories produced such ammunition for several decades. It was called .38/44 and was simply a .38 Special loaded to modern rather than blackpowder pressure levels.