4 barrel speargun....

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From the late sixties made by Tapmatic Corporation. There were single, double and quad barrel versions and a longer twin barrel Magnum version of the Johnson Submarine Gun (SMG). These guns use Ramset .22 ammo in a special plastic sleeve that waterproofs the cartridge and has a tip socket that holds onto the spear tail once it is inserted down the muzzle. The breech revolves open to extract the spent cartridge and insert a fresh one. Rather noisy and you are limited by the number of cartridges that you are carrying and the ones you happen to drop while reloading. A powerful shot, but such guns have been banned in many countries. The production went to New Zealand when another company purchased the design along with remaining stock of components.

A metal clip stored spare ammo on the top rear of the gun, you can see it in the patent drawing.


SMG TWO BARREL .22 cartridge speargun.jpg

Johnson SMG patent.jpg
 
The ammo came in different grades that were color coded, purple was the most powerful with yellow and green at the lower end. For the longer barrel Magnum versions there were even more powerful loads (see article below).
smg2.jpg

SMG brochure.jpg
 
I still have one of the 4 Barrel models.
It also had a Bang stick head for sharks or other large fish. I cannot find the bang stick head, it got lost during a move but I still have the gun and spears. When I was into snorkeling it was an amazing spear gun to own. I could hit those big fish that always stayed out of range of my other champion spear guns.

It was not until I got into diving that I realized the SMG had a Major draw back!
Contrary to what that article says I found that every 33 ft I went down with it almost halved the power of every type of shot, just like the pneumatic guns that I tried later on. At about 60-70ft it was no better than a two rubber spear gun and sometimes the cartridges leaked. I don't remember trying Silicone as a sealant as it was not popular back in those days, but I did use some form of rubber cement and that helped.
Eventually I ended up putting it in the closet because of that issue and also because I could no longer find a place to buy the plastic cartridges that it used.
 
https://www.shearwater.com/products/perdix-ai/

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