“Bouganville” improvised grenade launcing rifle
By 1943 the Japanese were experiencing “delivery” problems in their far flung conquests. In addition some supplies were not in the best of condition due to tropical conditions. The propellant charge for the T 89 knee mortar rounds was one such casualty.
From Page 53 of “The Knee Mortars of Japan” by White and Strange:
"The Bougainville grenade discharger rifle
In mid-1945 Australian troops captured seven improvised grenade launching rifles made by mating a Type 89 grenade launcher barrel and cut-off pedestal with a Type 38 6.5mm rifle with a shortened barrel. Humidity had affected the propellant charges in Type 89 shells, but the bursting charges and fuses were unaffected.
The shortened rifle barrel and shortened grenade discharger pedestal were welded together after a hole had been drilled into the cup of the discharger allowing the rifle barrel to protrude into the discharger barrel. T 89 shells with defective propellant charges had the defective charge removed and a hold drilled where the primer was normally. This allowed the end of the rifle barrel to protrude into the propellant cup. When the rifle was fired, with a blank or modified cartridge, the gases would force the copper band against the rifling imparting a gas tight seal much as the original propellant had done. The range of the weapon was reported as 30 yards to 300 yards."
Additional improvised launchers of varying design were found on New Guniea, New Britian, and in Burma. See the chapter on Improvised grenade launchers and rifles on p 199 in " Imperial Japanese Grenade rifles and launchers" by Babich and Keep.