Correct the crown is long gone. The barrel measures 4 13/16". It could only have been a 5" as the blade sight is still attached to the barrel.

Unless someone spot welded a blade sight and then ground it smooth. The barrel walls are almost 1/8" thick at 0.110".

Perhaps a 6" barrel cut down to match the length of the rib? Appears a bit wide for an almost 5" .38 S&W barrel.

My nickle-plate 1946 S 38 spl 5" barrel seems to be 0.095 at the muzzle.

Possibly the longer barrel was cut down specifically for the thicker walls w/intent on running higher pressure loads. Hot loads pushing 200 grains of lead could benefit from thicker muzzle walls.

It could happen. It's not as if I'm claiming this to be an OSS/M15 .38 S&W unregistered magnum. Although that would make for a whopping good tale.