MasterHunter

If you mean "how do you get the CT" what you must do is complete the Assignment Ada mingame (you can see it on the title screen) afterwards the CT will be available from the Merchant for 1,000,000 PSTAS.

OttoWottoBotto

Ok, to give you the most exact answer I can as possible, to not run out of ammo you really need to keep a handgun. As soon as you can get the BlackTail, it's the best of the handguns, upgrade it the best you can, and eventually if you can get a shotgun, either riot or striker, doesn't matter. Don't ever buy a rocket launcher or the mine launcher, they are a waist of money because they are crap. If you have the extra money, buy the Broken Butterfly because after you get it's exclusive it will have the highest firepower in the game, next to the fully upgraded HandCannon and both the crappy rocket launchers. The guns I suggested are the best because they easily get the most ammo, the rest are crap because of ammo shortage, and you get the Chicago Typewriter after beating Assignement Ada..not worth it, takes all the fun out of the game as does the Infinite Rocket Launcher and the HandCannon.