RT-20 sniper

The RT-20 is a Croatian anti-materiel sniper rifle developed by RH-Alan in the mid-1990s. The name itself is actually an acronym of the Crotian word Ručni Top 20 , or "Hand Cannon 20mm". Operating with a bolt action, it houses a single 20mm round and must be reloaded after each shot. Given its large caliber, it is one of the most powerful anti-materiel rifles currently in use by any country, and is comparable to the South African NTW-20 and the Indian Vidhwansak.
A unique feature of the weapon is the counter-recoil reactive tube or the back-blast above the barrel. This tube funnels gasses from the cartridge out the back end, similar to that of a recoilless rifle or rocket launcher.

This system is seldom used in small arms and comes with its disadvantages. It can not be fired in confined spaces, for example with structures, such as walls, in close proximity to the rear. Another disadvantage being the gases from the back-blast can be detected by the enemy and the sniper's hiding position is compromised.

It is also important to note that the maximum effective range of the RT-20 depends on the nature of the target.