The 645 and its successor the 4506 are just about the most rugged .45 autos you can find. Yes they are heavy and if you get slapped up side the head with one you are going to see stars and probably get something broken-on you never the gun.
I have a 645 that was modified by Novaks to have an interchangeable short slide & barrel from a 4516, an action/accuracy job for both slides and had the trigger guard rounded to the later style. It will out last the next few generations. They are pretty much the tanks of the handgun world. Mine looks a little off when the short slide is mounted on the full size frame, but it is a really good duty weapon, the 4513 (light weight frame) may be a little better for EDC, but I love my 645, with the long slide/barrel, it just looks real serious for real big gun. I have never heard a bad word about the 645.
If you want a DA/SA .45 auto, this is it.
