BSeed,
Basically you are correct on your meassurements. .45 is less than 1/2 inch and .50 is nearly an exact 1/2" diameter.
That .50 Cal rifle I mentioned is quite a piece. It could be fired off handed with out serious injury but that is more because of the weight of the rifle and its semi- recoiless design. The basic design is BAR with three times the weight. As a home defense weapon, you're better off with some ball bats and a few hormonal teenagers of both sex at final test time.
I have a hand loaded 45-70 Springfield Trap door that I shoot at paint cans with. Its so slow you can fire the rifle put it down and pick up your coffee before it hits.
Don