Anybody know...

EX-41 multi-shot grenade launcher, USA
(Also called China Lake launcher or NATIC)

Caliber: 40x46 low velocity
Type: multi-shot, cartridge-firing, manually operated
Overall length: 34.5 in
Weight: ~8.1 kg unloaded
Effective range: up to 300 m
Magazine capacity: 3 rounds

EX-41 is a manually operated, magazine fed grenade launcher. It has a tubular magazine below the barrel which holds 3 rounds, plus one round can be carried in the barrel. magazine is loaded through the port at the bottom of the receiver, empty cartridge cases are ejected to the right via ejection window. Reloading mechanism is operated by the sliding handguard, which shall be pulled to the rear and then pushed forward to complete reloading cycle. EX-41 was fitted with wooden buttstock that had a rubber recoil pad. Sights were of open type, same as on M79 grenade launcher.

The idea of a multi-shot 40mm grenade launcher came of a combat experience, gained by US troops in Vietnam. They were using single-shot M79 grenade launchers to great effect, but often found M9 to be too slow in reloading, such as in ambush / counter ambush situations. Therefore, US Navy (which was responsible for armament of various special purpose troops like Navy SEALs) set to develop such weapon. The task has been handled to the China Lake Naval Research Facility, which turned out first prototypes in around 1968. This large weapon represented a typical American-style pump-operated shotgun with tubular magazine below the barrel. Submitted for field trials in Vietnam, this weapon apparently performed quite well with HE-Frag ammunition, but often chocked on close-combat ammunition loaded with buckshot or flechettes (small arrows). This was mostly because of stubby shape of these rounds, while HE rounds had nicely curved noses which assisted reliable feeding. Furthermore, the overall weight of the loaded weapon was quite significant, to say the least. Apparently, no more than couple of dozens of such weapons, designated as EX-41, were made before US Forces were withdrawn from Vietnam. It seems that no further development has occurred on this weapon since then.

http://world.guns.ru/grenade/gl28-e.htm
http://en.wikipedia.org/wiki/China_Lake_NATIC
http://www.answers.com/topic/china-lake-natic

Its seems to be a grenade launcher (40mm in calibre) hybird in a reminton pump action shotgun so that three rounds of ammunition could be stored inside the chamber. As most gernade launchers are chambered for one round only, this unique weapon could have a higher firing rate by pump action....(like a shotgun).

是一枝槍...