I have 2 Young Guns now, but they have been shooting for several years. My question on him shooting the 9, is it just a few rounds or a mag, or is it shooting until you are out of ammo. A little recoil is fun for a few rounds, but 60 or so may make a very long day. A slicked up 73 is a great rifle, but weighs a lot more than a Henry .22. I had Widder Slick up our Henrys, they can be Very fast. My personal experience with the Stoger 410 is not so great. Good gun, but hard to load 2 smoothly and hard to shuck, an empty 410 doesn't have much mass to shuck with. Tried loading brass hull for it with only limited success. Then the kid tried a cut down 97 and has never looked back.
If I can help with anything, please let me know. Having my 2 boys shooting with me is something that I cherish. For the most part, they run better guns than I do, but if they are shooting with me, what else matters.