Polymer framed handguns do a good job of sucking up the felt recoil. The .45 ACP will feel a bit stiffer because it is lauching a 230 gr. bullet and the .40 S&W is launching a 155 gr. bullet. Honestly, you cannot go wrong with either caliber and both cost about the same if you buy factory ammo. The key thing is too practice a lot and become proficient, familiar with the handgun you do choose. I have both calibers and feel confident with either one, should the need arise. Shot placement is the most important thing to stop the threat. I don't worry about magazine capacity because the handgun will only be used until I can get to my Rem. 870, which is close to where I sleep and loaded with 00 buckshot.