I've loaded357, 44S/44Mag and 45-120 shotshells. Used the Speer shotshell caps in the pistols and used a gasket hole punch set to make overpowder wads for the 45-120 and a pair of scissors for the over shot wad.
Just figure the shot weight as the bullet weight when working up loads...437gr equal 1 oz of shot.
I also cut down some 20 ga plastic shot sleeves to go around the shot column which helped keep the shot together in the rifled barrel, but it still scattered more than in a smoothbore...just like a cylinder bore shotgun. I used #71/2 and 8 shot.
My experience was the same as BikerBeans. Shot a couple of chickenswith the 44Mag shotshells but they didn't seem to be bothered at the shot...just ruffled their feathers and look at me dumb...but the next moring they were lying dead on the ground just below where they were roosting when I popped them. At least the dogs had chicken dinner. Never caught a snake close enought to try the 44Mag's on.
The problem with the pistol cases is very few pellets, rifling and no choke.
The 45-120 cases held about 1 oz of shot I'm guessing and I used 800x powder...basically just fudged 28ga data from the Lyman shotshell manual, a cut down 0.070" nitro wad, filled the case with shot, covered with an overshot wad and used the seating die roll crimp The few I did shoot would kick up a nice dust cloud at ~25 yds and roll pine cones around. I think a 45-120 shotshell in a smooth bore would be similar to a 3" 410 shotshell or maybe a 28 ga....and a 444M would be likewise. Maybe #9 shot would work well also with a sleeve or...

Seemed like a lot more work to produce a shot shell than just using a shotgun or a plain old bullet so I only did a few just to see the happs....
I wonder if a screw on choke similar to T/C's 410 choke would work on a 45-70 or 444 M Handi? Maybe with some left hand threads to reverse the spin...I gotta think on this for a while.
Slightly OT...been fishing the last 3 days...limited out in trout (5 a day) every day, twice from the bank and once from my little electric motor boat...all planters from June...this from a small lake/res that has skunked me every time I went there (6 or 7 times a year)for the last 12 years. All totaled that was 18' 8" of fish...maybe I finally figured out HOW to catch trout. Hahahahahah
Luck