Have had a very nice very old damaskas double that is in excellent condition for many years but hesitated to shoot it simply because of the barrels. No doubt they would accept any load out there but I like a good safety margin for such things. A good friend was using light loads in a old double he had, 40 gn. Pyrodex ( by volume ) and 7/8 oz. shot with cardboard wads. I tried a few and while my gun seemed to handle them well, I took his lead and wanted to see how low one could go and still have a usable load. I stayed with Pyrodex RS 2F and tried two different loads, 30 gn. and 35 gn., both by volume, not by weight. I used one of those brass powder measures that are usually used with black powder rifles. Using Winchester AA cases, they were inspected and trimmed to two and a half inches. A sharp pocket knife was used to put a very fine chamfer on the inside of the cut off case. I have plenty of various cardboard wads but wanted to try something a bit different and dug out a old box of Herters Chalice wads. With a bit of measuring it was determined that they needed to be trimmed 3/16” off the petal end, this was done by eyeball with a small but sharp set of scissors. You may have to adjust this figure depending on case, shot charge, etc. Winchester 210 primers were used. Even though wad pressure is not normally used with this type of wad, I used 60#, loading was done on a old MEC 310 shotshell press and crimping was done using a Lyman roll crimper in a drill press. A 7/8 oz shot load is very light for a 12 ga. but decided to stay with it as it will also keep pressure's down and it might be such I will try a 3/4 oz. shot load. I want performance on rabbits and doves only and if you can hit them you can generally kill them. Didn't take too long to put together five rounds of each charge and even though it was snowing outside, out we went to see what would happen.
Noticed that the 30 grain load seemed very and I do mean very light. No recoil to speak of but it did seem to throw a good pattern at about 30 yards, one that would drop a bunny for sure. Trying the 35 grain load proved to be much more satisfactory. A nice good bump in recoil but not excessive at all, patterns still looked very good but the big thing was it felt very safe to shoot in the old double. I know flying by the seat of one's pants on what seems safe and what isn't is not the best way to go but I was comparing with some other custom black powder loads I had and the 40 gn. loads from the friend. Remember, I wanted lighter, not equal or heavier.
Loading up more of both loads I went out back to my custom laboratory ( the burn pile out behind the place ) and proceeded to run penetration tests on various cans at various ranges. The 30 gn. load , there again, just didn't seem to deliver. They would throw a good pattern all around the cans but most pellets ( ( #9 shot) failed to penetrate at 20 to 35 yards. The pattern was a good solid killing pattern with no holes but just didn't have what I would consider good penetration. Many pellets bounced off the bigger cans. The 35 grain load was the ticket. At 20 yards what it did to a can was very satisfying, no doubt it would take a rabbit and this performance seemed to carry out to 35 and 40 yards as well. The pattern opened up , of course, at the longer ranges but stayed very uniform with no holes that a bunny or dove sized bird could get through.
I do not think the 35 gn. load would have the necessary power for pheasants however. Our birds tend to be armor plated. I normally carry a 20 ga. with 3 inch mags and number 4's and a number of times I have blown feathers off with both barrels and the darned thing still flew into the next county.
The disclaimer. Most written instructions dealing with loading black powder shotgun shells talk only of using cardboard wads. Seldom do you hear of someone trimming a standard or in this case, a non standard plastic wad in order to make it work. I have used this technique in the past loading other shells and to date have never had a problem. The choice is yours. I tend to keep all my reloads, shotshell or whatever, more to the lower end of pressures and make up for this lack of power with good hunting. Get close and shoot em in the eye !! I feel these loads will prove to be safe in many shotguns but if you want to try it in one of the old twist wire doubles, have the gun looked over by someone who has an idea of whats going on and it wouldn't hurt to fire the first rounds with the padded gun sitting in a old tire and using a cord to fire it. These old guns are a lot of fun to shoot but it's tough to keep a smile on your face with missing fingers. Sneak up on all loads and be careful out there.