A pneumatic recuperator mechanism has a sealable valve which communicates a storage chamber with a displacement chamber; the mechanism includes a recoil piston which is connected to the gun barrel and is slidable jointly with a piston rod; the mechanism is improved in such a way, that with a predetermined built-in cross section a simple and light recuperator mechanism with a high heat-free operative readiness is formed.This object is achieved in that the displacement chamber 1 and the storage chamber 2 have the same inner diameter d and are arranged within only one cylinder 3, whereby the recoil piston 5 and the valve 6 are slidably received by the inner wall 4 of the cylinder 3. The valve 6 is advantageously in the shape of a disc and the recoil piston 5 is offset relative thereto. The valve 6 as well as the recoil piston 5 are provided with wear-resistant and delay-free seals 18, 24, 36 and guide bands 7, 23. The arrangement of the recoil piston 5 and the valve 6 permit a lower operative pressure level of the pneumatic working medium with a higher delay-free operative readiness.