May I ask why?
I was advised to buy a carbon copy of my carry gun. What do you think?
Not a bad idea. I have several Glocks, though they are not identical.
The idea is one to train with, one to carry. Or an identical backup in case one craps out. But I carry Glocks and don't worry much about durability. If I carried a gun with a more delicate constitution - a P7, 1911, Hi-Power - I might get an identical spare.
Writer Duane Thomas - excellent salesman that he is - recommends three identical guns: one on the hip, one in the shop, one on standby in the safe. Like most gunwriter advice, take it with an entire salt lick.