davey,
Went to the range this morning and took my 50 cal Huntsman, 24" barrel, not a Sidekick but close. Was going to try reduced loads with 44 cal 240 grain LSWC and T/C 50/44 sabots and FFFG Triple 7. THe 777 would not ignite, tried 3 times. Only other BP type powder I had was pyrodex 30 grain 44/45 pistol pellets. Okay why not? Loaded (2) of the pyrodex pellets and the 240 grain sabot bullet combo and hit the same POI at 50 yards as my regular load; 80 grain BH209, 45/50 MMP sabot, 385 grain .451 conical, winchester 777 209 primers. I then tried this reduced pyrodex pellet load at 100 yards and put 5 shots into a 3.5" circle, I am shooting with a red dot scope w/o magnicfication so that is about the best group I can get at 100 yards with any load. So this reduced load is probaby about the same velocity as my normal load - 1,400 FPS, light rain today so no chrony.
I did a quick & dirty penetration test and a 240 grn LSWC pushed by (2) 30 grain pyro pellets will go through a 3/4" tough as nails oak board, 3/4" of exterior grade plywood and 3/8" of standard plywood and keep going. Since the bullet went through almost 2" of wood I think it would go through a deer no problem.
I would equate the recoil to a 3" 410 shooting 3/4 oz of bird shot. Not really much to an adult, to a kid I don't know.
BB