I carry a Glock 30 SF (Slim Frame). It has a 10 round magazine. You should take your dad to a gun store and let him hold a lot of different guns to see what fits his hand(s) best and then look at different concealment options to see what combination will work the best for him. Even better, have him shoot a few of the smaller guns he is interested in as the smaller guns typically have a little more kick and are a little harder to hold sometimes. 45 is a great caliber though.