The gas-venting recoil mitigation system reduces the muzzle velocity of the 20x110mm Hispano cartridge by approximately 25%, from the original 830 metres per second to approximately 620 metres per second (from about 2,700 feet per second to about 2,000 feet per second).

The bracket on the right side of the RT-20 is a mount for a backpack carrying system, not a night vision mount as some online sources claim.

The RT-20's backpack carrying system consists of a frame with a matching lug that slides onto the gun, with two padded rests that support the gun muzzle-down, allowing soldiers to carry it via backpack straps with a quick-detach dovetail mount for storage.

The RT-20 uses a gas-venting recoil mitigation system consisting of gas ports drilled in the barrel that feed into a tube redirecting gas backwards, which both reduces muzzle velocity and creates a forward-pushing jet effect via Newtonian physics to counteract recoil.

The M55 anti-aircraft gun was a vehicle or tripod-based, three-barreled light anti-aircraft gun chambered for the 20x110mm Hispano cartridge.

The RT-20 weighs 19.8 kilograms (43.5 pounds) in its final production configuration, making it a very heavy weapon without obvious handles, so a backpack carrying system was developed to transport it.

The RT-20 is a 20mm shoulder-fired rifle that utilizes barrels from Yugoslav M55 anti-aircraft guns, which were originally chambered in 20x110mm Hispano cartridge.

The RT-20 is a single-shot rifle and cannot be reloaded from the shoulder by the shooter; it requires either a two-man crew or the gun to be put down to reload.

The RT-20 is not a recoilless rifle; it is a fully locked-breech bolt-action rifle with gas ports that operate similarly to revolver cylinder gaps, reducing pressure before it reaches the breech.

The recoil from the RT-20 is quite severe and the weapon has significant back blast, though not as substantial as a true recoilless rifle would have.

The RT-20 design was created by Ratko Janković, who was also responsible for Croatia's copy of the Milkor 40mm grenade launcher, manufactured as the RGB-6.

The RT-20 uses a Mauser-style bolt with nine locking lugs (three sets of three) and a Mauser-style striker system.

The RT-20 had no iron sights and was equipped with optical scopes, initially Khales 3-12x power scopes, with maximum practical range of approximately 600 metres.

The first examples of the RT-20 were manufactured in 1992, with proper regular mass production beginning in 1993.

The total number of RT-20s manufactured is unknown to McCollum, but estimated to be in the range of 100-200 units, as the weapon was only produced while M55 anti-aircraft gun barrels were available.

The RT-20 was used during the Croatian Homeland War, and a handful remain in the inventory of the Croatian army as well as some with various police SWAT units.

The RT-20 ammunition was typically high explosive rather than armor piercing, because the recoil mitigation system's 25% velocity reduction made armor piercing less viable, though high explosive remains effective regardless of velocity.

The RT-20 was not developed specifically to target the infrared sighting systems on Serbian M84 tanks, despite what many online articles claim; it was developed as a general anti-materiel rifle, though it was happy to be used against tank observation devices when needed.

If police come after someone with a 20mm RT-20, it indicates a response to a very serious offense.

The Croatians needed anti-materiel rifles in a variety of forms during the Homeland War, and manufactured several .50 calibre single shot or magazine-fed anti-materiel rifles before deciding to adapt the 20mm M55 barrels.