I own a CVA Dbl. Shotgun in 12 gauge. No choke in either barrel.
I found that I get my best performances using 2 3/4 drams( 75 grains) of 2Fg Goex Black Powder, and either a 1 1/8 oz load of #8 shot for Doves, or 1 1/4 oz. of shot for other upland game.
I load now using only OS cards, putting 3 cards on top of the powder, instead of one OP wad; then the shot load, and followed by 2 OS cards. All the cards have off-center holes poked into them using an awl, and I place the cards in the barrel so that the holes are 180 degrees opposite of each other. This lets air escape, but not small shot. I lube the barrel BEFORE loading the powder charge down the barrel, using a greased cleaning patch. The lube has been Young Country 101, but I am about out of it, and will switch to using Wonderlube. The lubing of the bore keeps the residue soft, but also stops lead streaks from being rubbed on the bore by the outer pellets. The grease in turns seems to reduce, if not eliminate, the flattening of the sides of those outside pellets, so that I get more uniform patterns, shot after shot.
The 1 1/8 oz- 75 grains of FFg powder load is a "Square load" combination- that is, the same volume of powder happens to also produce that volume of shot. My 1 1/4 oz of #5 shot however, is NOT A SQUARE load, as there is more shot by volume than powder by volume.
HOWEVER, this is the LONG RANGE load used by commercial duck hunters back in the 1870-'80's to kill ducks on the Illinois river near Peoria, out to 50 yards. I have taken pheasants out of the air out to a paced off, and witnessed, 33 yds with this load using my CVA shotgun. The heavy pellet, and its retained pellet energy at that distance is the key to success.
BP cannot produce the kinds of velocities we get using smokeless powder in modern shotgun loads. So, you have to shorten the maximum range at which to expect to kill game when using BP, and deal with the lack of choke in these guns when planning on how much shot to load.
I found in my load development that more (black)powder is not the answer- as it often is using Smokeless powder, BTW. In fact, I got better performance with my gun when I reduced the powder charge from 3 drams to 2 3/4 drams. :hmm: By better performance, I am judging this by smaller pattern diameters, fewer flyers outside the circumference, and more uniform dispersal of the shot within the circle of the pattern. Large Holes in a pattern, whether in the center( donut holes) or elsewhere indicate that something is NOT right with the load you are shooting. I got rid of holes by lubing the bore, and by stopping trying to use cushion wads.
CAUTION: Other members experiences surely differ from my own.