Which is the best wording to use at the range or in conversation?
Gat
Shooter, piece, heat,
Grip
You got the gats on deck brah
Toolie
Heston heater.
Ghetto population controller.
I prefer smoke wagon
Boomstick!
Racket, biscuit, and burner are all perfectly acceptable.
Ratchet*
Trust -I hate it when they ask to try out my cleaning rod in the rifle booth.
At the range "gun" is perfectly acceptable. "What kind of gun is that?" "Do you like that gun?" "Have you seen these guns?" (flexes biceps).

Heaters, IMHO.
Lead Dispenser
Brockback Mountain - You got the gats on deck brahLol

Whistle or chrome are both technical terms, as well.
As a pig, I can confirm we usually use the terms "whistle" and "heater" most often in our reports.
Don't refer to it as a weapon. That insinuates that it is used to hurt/kill people. It is a gun or firearm.
excerpt from one of my police reports:
"...As I approached the male subject, I observed a distinct bulge on the right side of his waistband. Based on my training, education, and experience, I know that gang members frequently carry burners concealed on their person. I know that the waistband is a common area for persons to conceal their gats. I unholstered my chromed up quad-nickel and pointed the business end in his direction. I instructed the subject to put his hands up or I would spit white-hot lead at him."
It's pretty technical language we have to use.