Cap and Ball Revolvers.

18 U.S. Code § 921(a)
(16)The term "antique firearm" means-
firearm (including any firearm with a matchlock, flintlock, percussion cap, or similar type of ignition system) manufactured in or before 1898; or
firearm described in subparagraph (A) if such replica-
States and which is not readily available in the ordinary channels of commercial trade; or
rifle, muzzle loading shotgun, or muzzle loading pistol, which is designed to use black powder, or a black powder substitute, and which cannot use fixed ammunition. For purposes of this subparagraph, the term "antique firearm" shall not include any weapon which incorporates a firearm frame or receiver, any firearm which is converted into a muzzle loading weapon, or any muzzle loading weapon which can be readily converted to fire fixed ammunition by replacing the barrel, bolt, breechblock, or any combination thereof.

https://law.justia.com/codes/georgia/2010/title-16/chapter-11/article-4/part-3/16-11-132/

OCGA § 16-11-132 - Possession of handgun by person under the age of 18 years

OCGA § 16-11-125.1 - Definitions
16-11-125.1. Definitions

As used in this part, the term:

(1) "Handgun" means a firearm of any description, loaded or unloaded, from which any shot, bullet, or other missile can be discharged by an action of an explosive where the length of the barrel, not including any revolving, detachable, or magazine breech, does not exceed 12 inches; provided, however, that the term "handgun" shall not include a gun which discharges a single shot of .46 centimeters or less in diameter.

Not what I wanted to hear but thank you. This article is very helpful.

I have a couple of black powder .44 revolvers and would not hesitate to carry them if 1) no other option were available and 2) I cleaned loaded and fired them daily to make sure they work. Sure you can store them loaded for a long time but when you try that first shot and nothing happens, you'll know why. With mine it was likely moisture that got in through the nipples. If you store them loaded you would need nipple caps.

That said they are fun to shoot and load. Both .44 and .36 round ball are still deadly projectiles.