Originally Posted by shotgunred
I am going to make the assumption that you will be using a glock. With that said if you buy a 9mm you can only shoot 9mm. If you buy a 40 or 357sig you can shoot the other with just a barrel swap. You can also shoot 9mm with a conversion barrel and the right mags. I would recommend you buy a 40 with the two extra barrels and some 9mm mags. I only say the 40 because if you want to sell the gun in the future it is a lot easier to sell a 40 than a 357sig.
I have a 357sig with a 9mm conversion bbl. I shoot both underwood and georgia arms in both calibers. The GA is "hotter" than federal, speer, etc and underwood is about 150fps faster than georgia arms. Both are priced less than the premium manufacturers like double tap and corbon. I spoke with the owner Kevin and he said that his business plan is delivera premium ammo with higher energy dump, better expansion at less cost than the others.
I shot a 5" group @ 10 yards with federal 125 gr and cut it to 2" with underwood. Great CS also. Loaded to what 357 sig should be. The 9mm gives both inexpensive range ammo AND the ability to have excellent self defence rounds in that caliber. The advice to buy a .40 and get two conversion bbls is excellent. You get three guns in one. If the shtf you will have three different calibers for you to scrounge for.