Hand Cannon 20mm: The Rucini Top 20
By Tom Murphy

Never let it be said that ordnance engineers won’t go to the most extreme measures to build a bigger, man-portable, method of destruction. The weapon presented here is the Rucini Top 20 anti-material, anti-armor rifle.

“Rucini Top, 20mm” means “Hand Cannon, 20 millimeter.” This unique beast was developed by the Croatians towards the end of the 20th century. It is manufactured in Croatia by RH-Alan and has been accepted by their army. It is also in use by Explosive Ordnance Disposal teams.

It is built around the Hispano-Suiza HS404 anti-aircraft cannon ammunition of World War II, which is still in current use for anti-aircraft work. The original cannon was also used on numerous aircraft of the United States, United Kingdom, France, and the ex-Yugoslavia. The projectile weighs 2,000 grains and leaves the muzzle at 2,900 feet per second. Effective range is 2,000 meters.

The action is single-shot with a three-lug bolt. The bolt must be removed for each shot, the empty cartridge removed and a fresh round inserted, which takes considerable time. However, the time spent reloading is about equal to the time spent in recoil recovery, so it really isn’t a factor. Optics are offset to the left to clear the reactive tube.

Due to the very heavy recoil of the 20mm x 100mm round, the RT-20 rifle design incorporates a one-of-a-kind recoil system. Generated recoil from the 20 kilogram rifle is approximately four times heavier than that from a Barrett M107, even with a large muzzle brake installed, so some sort of additional recoil system is necessary.

On top and in front of the action is mounted a large reactive tube connected to the barrel at midpoint. The rear part of the tube extends to the rear of the bolt action and the end cup forms a gas nozzle. When the gun is fired, a large portion of exhaust gasses are vented into the reactive tube and out the rear nozzle, forming a reactive force against the recoil. This type of design is similar to the Carl Gustaf Bofors m/42 20mm of World War II, and the American M67 introduced after the Korean Conflict.

This system of controlling recoil works well in larger rifled guns, but in the RT-20, it introduces some problems that are almost insurmountable.

First, and probably most important to the shooter, is the nature and position of the backblast. Care must be taken to insure that the backblast doesn’t set anything on fire, like backpacks, fellow military, or the shooter’s lower extremities.

Secondly, the RT-20, like other recoilless weapons of the type, cannot be fired in a confined area. Firing the rifle in a small room would likely kill everyone within.

Thirdly, position must be considered, as the backblast and muzzle blast combined will give away a shooter’s position to a much greater extent than most conventional weapons.

Truly a case of the old saying; “if a little is good, then a whole lot is way too much.”

RT-20 Rucini Top 20

Manufacturer: RH-Alan
Caliber: 20mm x 110mm Hispano Suiza
Service date: mid-1990s
Weight: 42.3 lbs
Length: 52.4 inches
Barrel length: 36.2 inches
Action: Bolt, single-shot
Effective Range: 2,000 meters
Sights: Optical, offset to left
Stock: Alloy/synthetic

This article first appeared in Small Arms Review V13N6 (March 2010)
and was posted online on April 27, 2012


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