The ZK-420S is an experimental Czech rifle that is virtually unknown today, but which was remarkably influential, bearing significant elements of the Garand and several other Czech designs, and influencing the M14 and Kalashnikov rifles. Originally designed by Josef Koucky in 1942, the plans were hurriedly dusted off and improved at the end of World War 2. With many nations looking at the possibility of adopted self-loading military rifles, Brno hoped to make export sales of the design.

The ZK420S uses the trigger mechanism of the M1 Garand and a gas operated rotating bolt action very similar to the Garand and AK rifles. It has a simple adjustable 3-position gas system, and a quick and simple disassembly procedure. It uses detachable box magazines (10 round, and not copied from an existing design) and was made in a variety of calibers for testing - including 8x57, 7x57, 7.5 Swiss, 6.5 Swedish, and .30-06. Examples were trialed or examined in the United States, Argentina, Israel, Ethiopia, England, Switzerland, Sweden, Norway, Denmark, and elsewhere - this particular rifle is from the Norwegian trials.

In my opinion, it is an excellent rifle, and its failure to sell was probably due to price and the combination of tight budgets and cheap surplus war material in the late 1940s. It is handy, well balanced, and has a good magazine design and good sights. Recoil is comparable to the Garand. Ultimately the development program in Czechoslovakia would lead to the ZK-472 in 7.5x49mm, which would proceed to the 7.62x45mm in the vz.52 rifle.