Originally developed as the PzB39 anti-tank rifle, the GrB39 was an attempt to keep the weapon suitably threatening to enemy armor. The original design, the Panzerbuche (armor rifle) 39, fired a sharply necked down 8mm cartridge, including both conventional tungsten/steel penetrators and an odd gimmick round intended to deliver a payload of poisonous chlorine gas to the interior of an enemy tank. Much like it's contemporaries it was unable to keep up with advancements in armor development, as the average plating grew too thick for a conventional bullet to penetrate. Adjusted to use a blank propellant cartridge instead of a live round, the Grenatbuche (grenade rifle) 39 could launch an armor-penetrating explosive warhead up to 150 meters. An internally threaded muzzle adaptor is attached to the muzzle, designed to fit the same pattern of grenade cup (not included) as the 98k infantry rifle, and a mounting point for a stacked wire crosshair front sight (not included) is fitted to the barrel behind the folding bipod and swiveling carry handle. The receiver has an applied plate over the serial number with the new model designation, and is fitted with a notch rear sight. The pistol grip doubles as the breech release, and the leather wrapped steel buttstock is hinged for under-folding and fitted with a padded, hinged buttplate.