It's funny to see the lengths people will go to in avoiding a .223. I was iffy on it at first. It's hard to have confidence in the little cartridge until you watch a bunch drop on the spot. I cleaned I don't know how many my kids and wife killed with it before I tried it.

Anyhow, one thing that happens when people get over the hill and lose near vision, is muzzle blast can make them flinch even if recoil doesn't. The pressure wave hitting the face is startling. Long barrels and cartridges that aren't extraordinarily high pressure at the spout are worth considering. Linear compensators and suppressors on short barrels are good, too. If he's left-handed, shooting a backwards automatic may be an issue. It'll for sure be louder.