As several have said, Speer makes the shot capsules for 38/357 and 44. Midway (1-800-243-3220) carries them for $7.29 for a box of 50. Depending on your usage, this is probably more than enough for a lifetime. Speer has loading data in their reloading manual. The main advantage of using the capsules is obvious when you consider the spread you'll get without them. I dare say a soda can would feel pretty safe at anything over 3 yds if nothing kept the shot together before it left the barrel.
Another advantage is that you don't get any leading as the shot travels down the rifling.
I always carry my Ruger GP100 loaded with 6 38 spcl shot shells when hiking around the snakey hills of western VA.