Hi Chris,I got one of these from a demolition clearance job many years ago(25+),it is a fire extinguisher,the cartridge is full of fire suppressant powder,if I remember the instructions correctly it says to aim below the fire and pull trigger and wait a few seconds,they are just like a huge centre fire shotgun cartride,to load the barrel has to be unscrewed a quarter turn which disengages it from the lugs,place in an antifyre cartridge and engage the lugs and turn to lock,pull back the hammer and it is ready to go,the pistol grip and works including the hammer are pressed steel,I assume it is powered by a slow burning small charge,I fired the one I had at the scrapyard where I worked and there is about a second delay then a huge "CHUFF" and the contents of the cartridge are discharged at the fire,it says to aim below the fire as there is a small ammount of muzzle flip,everything happens in slow motion including the muzzle flip,it all comes in a red tin box complete with gun and cartridges with instructions printed on the lid,I believe the powder caused the fire to be starved of oxygen but how effective they would be in a real fire I have no idea,Hope this helps,
Regards,Don,