I have a couple thoughts, the ammo subject has already been covered pretty well. i agree with the sentiment of keeping him with a revolver if that’s what he is comfortable with. I would suggest a fully lugged barrel all steel revolver. The extra weight helps keep the weight down. My Ruger SP101 is great for this application. A little extra barrel also helps add some weight on the end. Trigger jobs on revolvers are a piece of cake. There’s a great step by step guide on this forum, there’s some great videos on it, heck, I would be happy to help. A quick clean up and deburr does wonders for the action, without extra polishing and spring kit. That really smooths things up. Adjusting weight around can help a bunch too. Weight added to the barrel reduces muzzle lift, weight added anywhere reduces recoil. Attaching a picatinny rail under the barrel for weight attachment. I’ve heard of putting weights under the grips. I’ve seen tungsten grips or tungsten grip insets. A sheet of lead under the grips would add very little width but add a few ounces. I bet if you put all these together you’ll have a great revolver for him. With the add on weights and various action springs, you can get the trigger pull, firearm weight, and muzzle flip adjusted to where he can handle things like a champ.