Herr Kirkmeister: So that we are talking on the same page: There are 7000 grains to the pound, and 16 ounces to the pound. One ounce equals 437.5 grains by weight. In that small a caliber, or gauge smoothbore, ( .50 caliber) ( 37 Gauge) you want to start with reasonable levels of both powder and shot and work up. This is not a gun to use to shoot Geese or ducks, or even pheasants. Its a very small game gun, and because the bore is so tiny, the patterns are not going to be that good. Too many pellets are going to scrape the inside of the barrel going out of the gun, which will put flats on the pellet and make them slow down even faster. Only a few pellets in the middle will survive in any kind of round shape to make a pattern at anything over 20 yds. ( about 18 meters).
Start with the 5/8 oz. load that Joe suggests. That calls for an equivalent amount of Goex FFg powder of 50 grains. 5/8 oz equals 274 grains by weight in grains. That should be a good starting load, safe, and will give you good patterns out to 20 yds, or so. Beyond that, you are stretching the effect range of your gun. " Effective " is determined by shooting the load at paper, and inspecting the target. Shoot several shots at different pieces of paper, and at 20 yds, and see how many pellets make it to a core area of 10 inches. To determine what size shot to use, shoot at a soda pop can at 20 yds, and see how many shot of the size you choose will penetrate both sides of the can. When you find out what is effective, at 20, then 25, then 30 yds, you can go back to adjusting the amount of powder, and the amount of shot you shoot until you find a combination that gives you the most pellets on target that penetrate the furthest. That will give you your maximum range to shoot at birds, rabbits, or squirrels, and it will tell you how large the shot has to be in order to kill the game effectively.
I would not exceed a powder charge of 70 Grains of Goex FFg, and one ounce of shot. That would be considered a magnum load by anybody's standard, and probably won't put as many pellets on target as some of the lesser charges. The shot column that leaves the barrel of that small bore will be very long, and most of the pellets will be deformed and will be dropping to the ground before they reach 20 yds.
If you need loading data, look at any reloading manual for modern cartridge shotguns, and use the data for the 28 gauge guns. Just use black powder. I believe that Swiss 1 1/2 is equivalent to the Goex FFg powder, and that the Swiss #2 powder is equivalent to Goes FFFg powder. That means its burns faster, and creats greater pressure. Try the lighter amount of powder and see what kind of patterns you get. You may want to switch the Swiss 1 1/2 powder for this smoothbore.
Do not feel that this smallbore shotgun will handicap you. If the truth were really told, most birds are shot inside 20 yards, even ducks, and geese. And you should be able to walk within 18 meters of any rabbit. I have gotten to within 2 meters of a rabbit just walking softly and moving very slow. Good hunting.
