The Ukrainian design likely uses a recoilless gun concept, which hails from World War I's Davis gun.

This launched a counterweight backward at the same time as the projectile is fired forward, a technique which Moss dates back to the 1910s and the recoilless guns developed by Commander Cleland ...

Saab’s design was for a shoulder-fired recoilless rifle capable of firing 84 mm anti-tank ammunition. Recoilless rifles operate on the principle that equal but opposite forces counteract each other.