Try Iron Jim Rackham's idea of using only Over Shot ( OS) cards to load your gun. put small holes in the side areas of each card, back enough from the edge so that the edge does not collapse going down the barrel. Orient the cards so that each hole is covered by the next card. 12, 3,6,& 9 o'clock will do the trick. Seat those 4 on your powder charge. Start with 55 grains( 2 drams) and go up or down from there to see what patterns the best out of your gun, with the shot size you choose. 1 oz. of shot is going to be enough, and 7/8 oz should be just as good. Use two of the OS cards on top of the shot, one hole at 12 and the second at 6 O'clock. That will hold the shot in all day and then some.
To lube the barrel put a lubed patch on your cleaning jag( and loading jag) and either run it down the barrel as you seat those two OS cards on top of the shot, or simply lube the barrel with a second stroke after you have seated the OS cards. The lube will protect your barrel all day long, even in the rain, you will have enough lube to soften any fouling that might stay in the barrel on firing, and that fouling can be easily removed with a patch run down after each shot. You should get a little extra velocity with the barrel lubed this way, but the average velocity and SDV of your loads will be reduced considerably, giving you more consistent patterns, shot for shot. That is important, as many ML shotgun and smoothie shooters complain of not being able to get any consistency with their pattern.
Jim's reason for using the OS cards, only, is that since each is light weight, and the hole in each of them lets air separate the cards, they fall to the ground and out of the line of the shot fairly soon after leaving the barrel. The oiled, or lubed cushion wads--even the half wads some men are using - tend to follow the shot, and may blow the pattern into a donut hole, with little or no shot in the core circle of the pattern, but lots of shot in an outer ring. That might work for skeet shooting, but not for hunting.
All you can do is pattern your gun, and do your own testing. Use newspaper at 25 yds to test different loading components. Then move your pattern board back to 30 yds, to see what kind of performance you get with various combinations of powder loads and shot loads. Buy a can of the cheapest spray paint to use to put an aiming point on your paper. If you buy " Krylon paint " it will dry almost before you get back to your gun. Just a squirt of the paint in the middle of the target should be sufficient to replica most clay targets at that distance. I use black, but have also shot at blaze orange, and red. I don't think the color is as important as the contrast with the newsprint you use. I don't think I would recommend using light yellow or pink, or light green for this work.
In my personal experience, I have had full cushion wads actually hit the paper at 25 yards when I had lubed them with moose milk. I started using half a cusion wad and that helped. I still have to get out and try Jim's system myself. But, enough people here have tried it with good results for me to abandon using half cushion wads, and Over powder cards, and switch to using only OS cards, only. It makes taking components into the field a lot more simple. ( anytime you can use the KISS principle, you are probably much better off!)
OH, I almost forgot. Check the actual bore diameter of that new gun before you go ordering wads. My 20 gauge fowler barrel is oversized, and I had to order 19 ga. cards. 20 gauge is nominally .615. My barrel measured .627" Use a caliper to measure your bore diameter, and order the correct sized components. In my gun, the 20 ga. cards would not seal the bore, or hold the shot in place! They surely were easy getting down the barel, even without any hole in them to let out the air.
