Under no circumstances shoot that gun with modern/smokeless powder. If it is checked and OK'ed by a good 'smith then you could shoot it with Black Powder. They are excellent guns and some still see a lot of shooting with Cowboy action Shooters. I've know other Shooters to use an original '73 along with original SAA Colts. The .38/40 is pretty close in power to the .40 S&W that is the current choice of a majority of US Cops. At a reasonable range, I believe 100 yards or less it's plenty for hunting game up to the size of WT Deer.
BTW, if you shoot it with Black Power it has to be cleaned with soap and water.
You can go over to the BP and Cowboy forum here to learn more. Your gun may be worth quite a bit of money.