I bought this Blaster on a medal and militaria buying trip to England in 1980. My partner and I bought dozens of enlisted and officer’s full dress Royal Scots Greys uniforms with belts, gauntlets, pouches, boots and bearskin helmets that were being disposed of by the Regiment. We also bought lots of British WW1 medal groups that were sold for little more than the value of the silver. I bought this Blaster from one of the medal dealers who picked it up at a flea market in Uxbridge.
This “Blaster” is created from a S.M.L.E. rifle marked DP which means "DRILL PURPOSES ONLY." They were worn out rifles assigned the DP tag (that's why they became DP they were shot out) and further disabled to prevent firing.
This "CUP" style grenade launcher was designed in WW1 for use with the No.1 Mark III Short Magazine Lee Enfield Rifle, enabling it to launch a "Mills Bomb" grenade in an arc trajectory.
This can-shaped launcher would be attached to the muzzle of the rifle and a gas check disc was screwed onto the base of the grenade before the grenade was placed in the launcher. The safety pin could then be removed as the launcher cup kept the safety-spoon in place. The operator inserted the blank cartridge into the rifle before setting the stock, angled on the ground to absorb the recoil of the weapon. When the cartridge was fired it pushed the grenade out of the cup releasing the spoon. The cup-type launcher could launch the grenade about 200 yards.