I hate to say it, but I'm not much of a fan of 223 on deer size targets. That said, it would have little to no recoil. If you get @ a 7lb rifle any of those would have little to no recoil. That said, as mentioned before the 243 would be a good choice. Next for a pistol cartridge, I'd pick the 44 or even a 45 Colt. These would have excellent knock down power with little to no recoil. But if you're going to shoot more than say 100yds, go with the 243. You get him a good quality gun lever or bolt, it'll last him a lifetime