Been a very long time since I did one, but a .38 Special reamer was run into the barrel & then a throater reamer was run in to allow the 0.362" bullet to be chambered. It would help if you could have the barrel slugged to confirm the bore size. Remember, you should keep the pressures down to the original .38 Long Colt / .360 No. 5 Rook pressure levels, which, IIRC, is ~13,000 psi, NOT .38 Spl. levels even in a baby Martini, as cartridge extraction is always the weak link. I run my .298 Westley Richards Minex at ~17,000 psi. If I exceed 20,000 psi, then a fired case gets hard to extract. I presume the bore is nice? If not, then re-barrelling is likely your only option.