What this covers
During its Homeland War, Croatia manufactured a wide variety of ad-hoc firearms including a number of anti-materiel rifles. The RT-20 was the largest of these, and its development began with the discovery of a stash of Yugoslav M55 anti-aircraft cannon barrels chambered for 20mm Hispano in a warehouse. These barrels were cut down, fitted with single-shot bolt actions, bipods, and bullpup stock assemblies and became the RT-20s. The most unusual element of the design is the use of gas vents about halfway down the barrel which open into a hollow tube which vents over the shooter's shoulder. This creates a gas exhaust jet upon firing to help counteract recoil (and also reducing the muzzle velocity by about 25%). The recoil from firing is still pretty brutal, but the guns can be used - and were during the war for Croatia's independence. A few remain in Croatian police inventory today...
A big thanks to the Croatian Police Museum (Muzej Policije) in Zagreb for giving me access to film this rare piece for you! Check them out at: https://muzej-policije.gov.hr
http://www.patreon.com/ForgottenWeapons http://www.floatplane.com/channel/ForgottenWeapons
Cool Forgotten Weapons merch! http://shop.forgottenweapons.com
Source description (no synthesized summary yet).
The RT-20 is a purpose-engineered anti-materiel rifle that uses a gas-venting recoil mitigation system, not a recoilless design, to make the 20mm Hispano cartridge shoulder-fireable by Croatian forces during the Homeland War.
- The RT-20 uses a fully locked-breech bolt-action mechanism with gas ports that reduce pressure and vent rearward, fundamentally different from recoilless rifles which vent equally in both directions
- The system reduces muzzle velocity by 25% (from 830 to 620 m/s) to manage recoil, making it minimally viable as a shoulder weapon rather than an ideal design
- The weapon was purpose-built to utilize available Yugoslav M55 anti-aircraft gun barrels and fulfill the Croatian need for anti-materiel rifles, not to specifically target Serbian tank IR systems
This asset isn't compiled yet
You're seeing its claims, ranked. Compile it to build the argument threads, weight them, and check each claim against your library — the full view.
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 ammunition used with these was typically high explosive rather than armour piercing, because this whole recoil mitigation system takes about 25% off the muzzle velocity of the gun... High explosive doesn't care how fast it's going, and it's still quite effective.”
The M55 anti-aircraft gun was a vehicle or tripod-based, three-barreled light anti-aircraft gun chambered for the 20x110mm Hispano cartridge.
“Typically it was a vehicle or tripod based, 3 barrelled light anti-aircraft gun chambered for the 20x110mm Hispano cartridge.”
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 origin of these starts with a supply of Yugoslav People's Army anti-aircraft gun barrels that the Croatians got their hands on. These were barrels for the M55 anti-aircraft gun.”
The first examples of the RT-20 were manufactured in 1992, with proper regular mass production beginning in 1993.
“The first examples of the RT-20 were manufactured in 1992, with proper regular mass production beginning in 1993.”
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.
“At any rate, they were used during the Croatian Homeland War. A handful of them are actually still in the inventory of the Croatian army, as well as some with various police SWAT units.”
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.
“You have this backpack frame with a matching lug right here that is going to slide onto the gun. And voilà, you have two (even these out) you have two backpack straps here. The gun is carried muzzle down on these two padded rests. So that's how you would actually move it around. And then this has this quick-detach dovetail mount for when you need to store it or take the backpack frame off.”
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.
“what he did was put gas ports in the barrel here, and then build this tube that redirects gas backwards out the back end of the gun to do two things. First off, by putting ports in the barrel here, you are reducing the muzzle velocity of the cartridge, which is going to reduce the felt recoil from it. But it's also taking that gas and instead of redirecting it to, say, operate a semi-automatic action, it's just blowing it out the back of the gun. And basic Newtonian physics says that if you are pushing a bunch of gas back that way, the gun is going to be pushed forwards.”
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.
“this is a gun that weighs in its final production configuration here, 19.8 kilos. Which is like 43.5 pounds, that's a really hefty gun. And there are no real obvious handles on it, so how does one carry it around? Well, they came up with a system for carrying it around.”
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).
“this whole recoil mitigation system takes about 25% off the muzzle velocity of the gun. So where 20x110 Hispano was originally 830 metres per second (about 2,700 feet per second), with this setup you are getting about 620 metres per second (about 2,000 feet per second), so a significant reduction.”
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.
“this is a single-shot rifle... this is not the sort of thing you can reload by yourself from a shooting position. You would either have a two-man crew operating the gun or you just put the gun down, open it, extract the empty cartridge, put in the new one.”
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.
“And the recoil from these things is quite severe. So there are a few videos out there on the internet, they aren't mine, I can't include them here. But if you do a quick search on YouTube, you'll find a couple of videos of guys actually shooting these. And they are not recoilless, there is a lot of recoil to them.”
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.
“This design work was done by a guy named Ratko Janković. He's actually also the designer who is responsible for Croatia's copy of the Milkor 40mm grenade launcher, which they 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.
“We have just a pretty simple basic bipod in place. Looking at the back end of the gun you can see the exhaust cone here... We have a Mauser-style bolt here, nine locking lugs on it.”
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.
“In terms of mechanics, as a bolt action there's nothing particularly unusual about the RT-20. Moving up here a bit we have the sighting system, there are no iron sights on here, they all have scopes. And it's a very simple system, there's just a big block bolted onto the side of the exhaust tube block, the gas block I suppose you could call it, a pair of scope rings. Initially these were fielded with Khales 3-12x power scopes.”
The RT-20 would be unsafe to operate indoors, as firing would cause significant deleterious effects on the building and the shooter due to back blast.
“And this isn't a weapon that can be operated indoors. If you're in a small room and you fire one of these things off, it's going to have significant deleterious effects on the building and the shooter.”
The muzzle brake on the RT-20 is described as 'ginormous' and is bolted onto the weapon to attempt to reduce recoil impact on the shooter.
“There is a ginormous muzzle brake bolted onto this thing just to try and reduce the impact on the shooter, again it's a huge cartridge.”
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.
“you will find a lot of articles online that describe how this was designed specifically to target the infrared sighting systems on Serbian M84 tanks. That's not true. I'm sure they were happy to use them for that role, but they were not developed specifically for that. They were developed as anti-materiel rifles, because the Croatians wanted anti-materiel rifles in a variety of forms.”
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.
“what they really needed were anti-materiel rifles. The Croatians manufactured a number of .50 calibre single shot or magazine fed anti-materiel rifles. And they decided that they could make use of these 20mm barrels to do the same thing.”
The RT-20 is described as an 'ad hoc' firearm from an engineering perspective, designed to solve an immediate problem using available materials rather than as an ideal design.
“Engineering-wise it's a really interesting ad hoc sort of firearm.”
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.
“Now people will often look at this gun and describe it as a recoilless rifle. Now that's really not true, there's a vague similarity in the concepts, but with a recoilless rifle the idea is that the cartridge case itself is actually perforated and doesn't hold pressure, and gas vents equally in both directions.”
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.
“unfortunately I don't know a total number of these actually manufactured. This one's numbered 154, this isn't the sort of thing that there were thousands made of. But I don't know, 100, 200, something in that realm.”
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.
“there's one other really cool element on here that I want to point out, and that is this bracket on the right side of the gun. You will see various explanations for that online, people say it's like a night vision mount. That is actually a mount for the backpack carrying system.”
The gas ports in the RT-20 barrel are located at approximately the same position as the gas block on the original M55 anti-aircraft gun system, suggesting the Croatians may have simply cut down the M55 barrels and left the gas ports intact, or separately drilled matching ports.
“Now to be honest these gas holes look like they are at about the same position as the gas block on the M55 anti-aircraft gun system. So it might have been the case that the Croatians simply cut the barrels down, left the chamber intact obviously, and then also left the gas ports intact and used that to locate their gas block. Or they might have drilled these separately, I'm not sure.”
The gas block of the RT-20 has a serial number (154) marked on it, which is visible during inspection.
“The only marking on here is this serial number, 154, on the gas block.”
If police come after someone with a 20mm RT-20, it indicates a response to a very serious offense.
“If the police come after you with a 20mm RT-20 I don't know what you did wrong, but it warranted a response.”