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Johnson Submarine Gun (SMG) cartridge powered

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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popgun pete

Well-Known Member
Jul 30, 2008
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.
SMG brochure.jpg


SMG Reel.jpg

Johnson SMG patent.jpg
If you look carefully at the patent drawings then you will see that the SMG trigger mechanism is just a pull down sear lever mechanism, as was used in the first French Arbalete, which fires a long captive bolt that acts as a firing pin. Until I found the patent the innards were a mystery to me, but coincidentally in my own cartridge gun I used a similar mechanism based on a spring gun trigger mechanism which operates the same way. Unfortunately when the rules changed I had to destroy it, however it was not a very practical weapon, but seemed a good idea at the time.
SMG handle and trigger mechanism.jpg

Ramset .22 spear pistol 2.jpg

My ramset pistol for underwater hunting, built in the early seventies. The bolt is cocked by drawing the top lever back and then moving it sideways in a dogleg gate which acts as a safety. You inserted the shaft, which was retained by an internal collet at the rear of the stainless steel tube barrel, and then put a ramset cartridge into the breech. The breech was then screwed shut with about 3 turns of the barrel, the line was rigged and once you were ready you flipped the lever upright and you were then ready to shoot.
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This time you gave me one double barrel I still have it on Craigslist right now and some dude wants to buy it for $5,000 how much are they really worth oh my God so far I've seen it up to $10,000 somebody tell me what they are worth please double barrel smg-e made in California
Worth depends on who wants to buy it, with no ammo and banned in many places there would be few people who want one bar collectors.
Some photos of the ammo showing the washers and sleeves. On these examples you can see slots in the front end that may have helped pushing the spear tail in the front end if the plastic used was not compliant enough to stretch and allow trapped water out of the front cup.
smg sub ammo photos.jpg


SMG Sub Ammo.jpg
Note that Ramset .22 cartridges are/were colour coded by a dab of paint on the crimped front end of the wadded blanks; you just selected a plastic sleeve of the matching colour so that you could identify which load you were using as once glued into the sleeve you otherwise would not be able to tell.
This image shows a comparison of the long barrelled MAGNUM model and the standard MKII, the MAGNUM being able to use the more powerful ammo grades with the extra barrel length allowing more gas expansion inside the confines of the barrel to drive the spear.
SMG MK II MAGNUM and Standard model.jpg
As I have cleaned up the patent drawing for another thread here are the innards of the SMG. When you pull the trigger the sear lever drops out of a notch and the sliding hammer thus freed moves forward to strike the firing pin. As the speargun uses rimfire .22 Ramset cartridges in their special air gap plastic sleeves the pin hits on the cartridge rim. The sliding hammer has two notches for the sear lever tooth to engage, one for cocked and the other for fired. The SMG breech is pulled forwards slightly and revolved on a pivot pin to expose the breech opening above the axis of the gun, you put the cartridge in and swivel the breech back down to the in-line and lock position by pulling the outer ribbed cover back. Hopefully the fish you want to shoot is still hanging around if you missed with your first shot. Lose your grip on the SMG gun and it will head straight to the bottom, so really more suited to scuba users. Another problem is dropping the Sub Ammo while carrying out reloading operations as you can only carry so many spare cartridges, the gun itself has provision for four in the rear clips and one in the breech ready to go.
SMG shooting operation.jpg
On my gun, which was inspired by the SMG, although I had never seen one and then knew nothing of its innards, I used the same pull down sear lever trigger mechanism made from chromed brass using ideas copied from a Cressi-Sub spring gun. The sliding bolt was a cylinder bored at the rear end to enclose part of the biasing coil spring and the firing pin was fixed. To undo the stainless steel breech you had to cock the gun and rotate the firing bolt’s control lever into a dog leg in the draw gate, otherwise the firing pin would stop the breech revolving. The breech was very strong being machined out a propeller shaft section, the rear section of the stainless steel breech was screwed into a cylindrical chromed brass body with flow ports along its length to prevent hydraulic lock effects. This metal body was fixed by two big stainless steel transverse pins that attached onto a stainless steel, rectangular cross section, vertical bar that ran the full depth of the timber handle and made the gun very heavy. The timber body was resin impregnated in an autoclave and was also heavy, it being assembled from two halves bonded together with a separate top section. The gun was to carry a small reel on the rear deck, but that was not proceeded with. The gun barrel was precision bore stainless steel tube made for high pressure applications and the muzzle tip was chromed brass with line winding hooks that also allowed something to grab onto when unscrewing the breech with your fingers.

The gun was a bit of a disappointment as it really needed an air gap for the explosive gases to expand into, although the breech was long enough as I designed the gun not to blow up and resist any recoil of the gun body. I destroyed it by cutting through the breech with a hacksaw, cut up the barrel and threw everything else out, keeping only the trigger mechanism which had been cut from brass plate using a hacksaw and filing it to the final shapes. All pivot pins were 316 stainless steel rod, as were the nuts used to hold the passive line clips and breech pivot pin that allowed the breech to tilt forwards for reloading the gun with another cartridge. All cartridge powers could be used, although I never tried the purple Ramset loads as they had a different cartridge form.

The breech used a coarse screw thread cut on my lathe, it was not a standard screw thread and was a difficult cut when doing the female thread section using a special boring bar to reach into the cavity. I made two of these guns, the other went to my buddy who passed on many years ago.
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Here is my correspondence with Valerie Johnson which resulted in their reply.
Tapmatic Reply.jpg

More to follow.
When Tapmatic sold off the SMG to New Zealand all the paperwork records went with it, but Valerie had kept photocopies and that is what he sent me. The original of this was printed in red and black, but I threw my original out years ago when the SMG was put on the prohibited weapons list.
SMG Brochure page 1R.jpg

Good to see the old advertising traditions continued back then; male diver in full wetsuit and lovely companion in something more revealing.
The next page, the brochure was folded into three panels from memory.
SMG Brochure page 2R.jpg

Sometimes it was hard to focus on the guns!
The next brochure. Might not have this paired right as my memory is the photos straddled the fold in the page, but this will have to do for now. Can fix it later if needs be.
SMG Brochure 3R.jpg
The first SMG was the single barrel model, it is the only gun that I ever saw in the flesh so to speak, sitting on the glass counter top at Alcock and Pierce, a sports store in Melbourne. It was smaller than I thought it would be, but I didn’t pick it up to check the weight. I think they wanted 150 bucks for it, but at the time the regulations were closing in and for sure the SMG would have to be surrendered once they were finalised. That was only months away, spurred on by a mass shooting which was used to mop up a lot of weapons. That would be just a drop in the bucket compared to the next crackdown, but that was in the far future back then.


The next model was the SMG Double Barrel version. The idea was to use a standard spear in one barrel with a shooting line, and the second barrel could have another spear, either a free spear or one equipped with the SMG powerhead. For heavy duty work the guns had a game reel attached on a plate straddling the two handgrip butts. As you don’t want two lines in the water it was a situation where you may have to kiss goodbye to the free shaft if you happen to miss. To offset some of the weight with the extra barrel and larger breech a buoyancy element was inserted between the barrels as an extra fitment. Rotating the breech through 180 degrees brought the next barrel to bear, the bottom barrel is the one that fired.
SMG Double Barrel with powerhead fitted.jpg

Extra ammo could be carried on the clips at the rear of the gun, there was provision for 4 extra cartridges. Carrying cartridges was a problem as they were easily dropped, ditto for the sparklet CO2 guns such as the US Divers “Sea Hunter” pistol.
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Somewhere I have filed the Tapmatic cover letter in a place so secure that I cannot find it, but for sure I have not thrown it out. For now you can read the follow-up conversation with Valierie Johnson. Got the spelling right this time!
SMG Correspondence R.jpg
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