I suspect most of us have tried this over the years with varying degrees of success.
My own best attempts came about when I made a shot cartridge of sorts, or maybe it could best be called a "enclosed wad" in order to keep the shot away from the rifling.
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I used a plain brown paper bag, cut an appropriate square from it, ie 4" x 5" rolled that square of paper on a wooden dowel of a size that allowed it to load easily down the barrel, glued the rolled edge, removed the dowel, allowed the rolled paper to dry, poured in an amount of shot that was equal to the amount of powder being used, folded the ends of the paper roll over gluing one end and twisting the other with a small extended 'tag'...and it was ready to load.
I still use this so-called "shot cartridge" at times in both of my smoothbores.
Of course, in a smoothbore it is strictly for convenience and speed of loading, while in a rifle it does seem to help hold the pattern together a bit longer.
To the best of my knowledge there is no sure fire way of shooting shot through a rifled bore and achieving good patterns, without jumping through a few crazy hoops.
Still yet, it can be done with a moderate amount of success, and it can be a lot of fun.
This question has been asked a lot over the years, and it begs for a better answer than the one I have given.
I have read of others doing different things, and I must have tried dozens and dozens and dozens of different ways myself, but this method, for me, has served the purpose best.
I can't prove it, but I strongly suspect that the use of 2F powder is preferred over 3F when using shot because you do need a OS (Over Shot) card when you seat your shot cartridge....and 3F "appears" to give more blown / erratic patterns than 2F.
This is just an observation on my part and may only happen in my guns, but I have suspected this to be true for years on end, but I can't find anything that agrees with the theory.
Uncle Russ...