If it is in shape fit to be fired, commercially available 38-40 ammo will do. It is loaded to pretty low pressures, based on the premise of being safe to shoot in the weakest firearm that it is likely to find it's way into.
If your gun is a Black Powder rated gun, you will have to be doing some homework and reloading, or track down some appropriate low pressure loads.
On the plus side, the Cowboy Action Shooting guys and gals have created a market for light loads of ammunition that may be what you are looking for.
There are a couple powders, like Trail Boss, for one, that are more appropriate for loading loads that are approximate to the same as black powder loads, as far as smoke and noise go, that may be worth the time to look into.
Oh yeah! Pictures! If yer gonna brag about a score like that, pictures!
Cheers
Trev