I have both a K9 and a K40. I sent the 40 into Magnaport hoping to tame the flip some. I think it helped a bit but still a lot of flip. Many have no issue with that at all and love them. I carried it for years, my first Kahr but just never cared for the jolt. It's not uncomfortable and I can shoot it all day, just kind of slow for a second shot I guess.
I use it now mostly for a grip model.
That being said I'd say if the old man wants a 40, he should get a 40. Your correct in that during the ammo shelf panic clearing there was usually still 40, so that's a plus. After accidentally loading a 40 into my brand new Magnum Research 1911 I gave away a ton of 40 ammo, which in hindsight was a terrible mistake.
Years ago I had a Glock 27 the compact 40 and it was a good shooter. For some reason the tupperware must have soaked up some of the recoil. I actually had a few of them, kept selling them to cops and there was another panic of some sort and they were hard to get even for the officers.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."