I like to KNOW my guns, inside and out. I am also incredibly adept at tearing things down and remembering which way they go back together. (Too much time with LEGOS, Tecnix, and Erector sets!) Even though I've only done it twice, I can tear a 1911 down to pieces and put it back together. Glocks are the same. Bolt rifles are all simple, just variations on the old Mauser theme. (I once "shot" a bottle of Hoppes with the firing pin from my VZ-24. Those suckers have ALOT of tension on them!)
The only guns that I know inside and out ballistically are my hunting arms. The 20ga 870, the .260 Mountain Rifle (I can put the bullet exactly where I want it from 0-300 yards and not blink, without a bench or bipod), and the Ruger 96/44 I used to have (traded later on after the .260 came home).
With handguns I feel like Tom Selleck's character in Quigley Down Under: "I only said I never had much use for one, not that I don't know how to use one."