yep , what Dan states is true .
the over powder cards are often very hard and wont easly go though a full choke . BUT if you split them they will go past . so in a since you will use 2 or 4 over the powder cards by splittin 1 or 2 full cards
im not much for chokes unless they are jug chokes for the very reason Dan mentions .
again though , they will do the same thing as with a centerfire . but as i said you can do that without a choke as well
here is a couple links to help you out
Black Powder Shotgun basics The Versatile Smoothbore ok , here are some loads for ya for a 12 gage
all these are for goex 2F
1oz , 71/2 lead shot
2), over powder cards
1), 1/2 fiber cushion
1 oz shot
75 grains powder . MV =1090 PSI -1200
80 grains Mv 1160 PSI 1500
11/8 oz shot
75 grains = MV950 PSI = 2700
80- grains = mv 980 PSI-2900
11/4 oz shot #4
75 grains MV =840 PSI=220
80 grains MV 900 PSI 3000
11/2 oz #4
75 grain MV-not listed , PSI not listed
80 grains MV =800 PSI 3600
1 oz #2 steel
75 grains MV =980 , PSI=2700
80 grains MV=1000, PSI 3000
1 1/8 shot #2 steel
75 grains MV = 960 , PSI 3700
80 grains MV=1030 PSI=4400
11/4 oz #2 steel
75 grains MV=830 PSI=2100
80 grains MV=890 PSI 2100
1 1/2 oz #2 steel
75 grains MV not listed PSI not listed
80 grains mv =780 PSI 2400
round ball load for cylinder bore
70 grains FF, .690 rb, 494 gr = FPS 794 ME 693 ,PSI 3000, FPS @100 - 683 ft lbs @ 100 = 512
80 grains MV 881 ME=852 ,PSI 3300 ,fps@100 750 , Ftlbs @100= 617
90 grains MV=962, ME=1015, PSI= 3700 Fps@100= 805 Ftlbs@100 =710
100 grains MV =1043 , ME=1194, Psi= $100 Fps@100= 850, ftlbs@100=792
hope that helps ya