You would probably get better ignition with Pyrodex P, rather than the RS, in your gun, with percussion cap ignition, but that doesn't help you get rid of your RS.
Try using a small charge- 10 grains of real black powder-- down the barrel first, as an "igniter" charge, then complete the powder charge with a small charge of RS. The two charges together should occupy the same Volume that you current charge of RS uses, BTW. That way you will get a similar performance in the barrel. I have been using FFg in my 12 gauge- only 75 grains( 2 3/4 dram)with 1 1/8 oz of #8 for dove, and 1 1/4 oz of #5 for pheasants, chukkar, and anything else legal to shoot that busts out in front of my gun. Both loads are good to 30 yards in my gun.
I am going to order a pound of Fg Goex to try in my shotguns, based on BrownBear's experiences with this powder in his guns.
All guns are different. There simply is NO shortcut to avoid doing a lot of work with paper at the range, patterning loads. Don't even think of it. BTDT. You need to not only have a load that patterns well, but you need to know where that pattern strikes(POI), compared to where you point the gun(POA). Use butcher or wrapping paper if you have it. If not use, newspapers. To find the holes, use the backside of the paper where the edges of the paper around the holes will stick up. An oblique light shined across the paper will highlight these "crowns", making them easier to "see", and circle with a magic marker.
At 30 yards you are looking for the amount of shot contained in a 20" circle, approx. It will be a very rare smoothbore that puts the center of its pattern at your POA. Second, you are wanting an even distribution, without huge holes in the pattern that might allow game to escape, or " fly thru" your pattern. :thumbsup: