These SMG spearguns first came out in the late sixties and I remember checking out the single barrel version at Alcock & Pierce which is/was a sports store in Melbourne. The ammo that they used was a limitation as although based on the range of Ramset .22 cartridges for power tools like nail guns, you needed the "Sub Ammo" plastic sleeves that waterproofed the rimfire cartridge and which the tail of the spear stuck into at the front end in order to stop the spear falling out of the speargun's barrel. They were non-floating after the shot weapons and more suited to scuba divers conducting spearfishing at depth. Tapmatic Corporation in the USA manufactured them for about ten years, then at some time Crocket and Co(?) in New Zealand bought the rights and the remaining stock of speargun components and subsequently produced the SMG in New Zealand. Being banned nearly everywhere but the USA destroyed the market for such guns. Tapmatic told me that they produced about 2500 guns, but how many more were made or assembled in New Zealand is unknown. I have seen a couple of the New Zealand guns and they are identical to the US guns being the twin barrel versions. These guns turn up every now and then on auction sites and are generally in good condition as they could rarely be used if you did not have the plastic ammo sleeves.