New Seac Shotgun

[popgun pete]

Recently looking at the Carbon C4 "Mr Dark" it would be interesting to see if an analogue could be made based on the Seac Sub "Shotgun". If a bulbous air tank could be grafted into the lower rear section of the gun to provide the same belly shape this would make an interesting gun in terms of tracking while mainting a more normal compression ratio, but how to do it? Some time back we saw a gun with an air tank in a rectangular block under the rear of the gun which itself was narrow, but nothing more was heard of it. From memory the name started with an “S”.

 

[popgun pete]

The gun I am thinking of was discussed on this forum, from memory the tank connected to the butt of the grip handle and was a rectangular shape externally, but had a bunch of interconnected tubes inside it for the pressure vessel. I remember having misgivings about the tank busting off the gun, but it certainly was different. It had its own website where you could order a gun, as they seemed to be built to order, and had been reviewed in a few places on the Net.

 

[Diving Gecko]

Was it the one that looked like a "normal" arbalete? With a wooden stock?

Making a buoyancy belly can be done by glueing foam onto the reservoir, shaping it and the covering it in carbon or glass fiber. The Carbozzi guns are made like this. Some of them use the Palengas foam wings as a starting point.


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[popgun pete]

Was it the one that looked like a "normal" arbalete? With a wooden stock?


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Yes, I think it had a timber stock, it was a pneumatic in operation, but had the body of an arbalete and from memory pre-dates the "Airbalete".

 

[Diving Gecko]

Yes, I think it had a timber stock, it was a pneumatic in operation, but had the body of an arbalete and from memory pre-dates the "Airbalete".

Yeah, it seemed to me that it wasn't a production gun but maybe just a tinkerer making a few of them.

As you know, I'm hoping one day to actually make a one piece reservoir like this (slim front with a belly). I think it'll be more voluminous than the standard compression reservoirs. But if anything, that should only be an advantage, right? I mean, the power curve won't taper off near the end of the shot. And I'm thinking, it's normally the force right at the latching point that gets me sweating. Even if it doesn't start much lower, that's probably not the big issue.
But if it has a Mirage system in it, that's a mute point. But if I get this reservoir made, perhaps the first one will be standard loading.


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[popgun pete]

The larger the tank volume to barrel swept volume then the better as the compression ratio approaches 1.0 as Vb/Vr becomes very small.

CR = initial volume divided by final volume or (Vb + Vr)/Vr = Vb/Vr + 1

I was looking for this odd-ball gun, and I am sure that I have filed it somewhere, as I was thinking of how to attach a “piggy back” tank pack under the Seac Sub gun without weakening the existing 40 mm diameter rear tank. From memory the arbalete style pneumatic gun had a bunch of interconnected tubes side by side in its rectangular shaped tank block and something like that could be curved under the main tank here. A sketch shows three tanks in a curved outer shroud underneath the gun looking back from the muzzle. These sub tanks being cylinders they will hold the pressure, the problem would be to interconnect them without causing throttling at the interconnections.

 

[popgun pete]

It just came to me, Santino, and sure enough I kept the info on it. https://forums.deeperblue.com/threads/arbalete-pneumatico-santino.106361/

 

[popgun pete]

They are still in business, but the gun has changed somewhat, looks a bit wider in the body than it was before.

http://www.arbaletepneumatico.com/

 

[Xape]

Thank you for this thread guys. I want to thank especially Popgun Pete for his great in depth content in several thread regarding pneumatic spear guns. I am an engineer and the subject is fascinating to me.
I also ended up buying a Shotgun 90 at the sale price link earlier in the thread. Here are my observations from using it a few dives and also about a problem I encountered .
First there is a mistake in all the Seac catalogs i found regarding the length of the shaft the Shotgun 90 comes with. It does come with a 100cm 6.5mm tahitian shaft (not a 88cm as stated in all the literature). The 88cm shaft comes with the 75cm gun. Since I also have a such a 88cm shaft I tried it in my Shotgun 90 and it did fit with minimal overhang. Even with the shorter shaft the gun is a bit nose heavy in the water, while with the 100cm it is quite more nose heavy.
After about a dozen of shots I encountered the problem that can be seen in the photos. The gun began to be very difficult to load, I thought the piston was getting stuck. When I got home I noticed that the cone shaped shaft adapter has become quite deformed in it's front side. It was fully threaded in, but did unscrew very easily by hand. The only reason I think how this came to be is the adapter hitting the steel washer, but I would have noticed it. The gun is not overpressurized (actually it's at quite a low pressure), nor did I have any line release issues. Isn't the washer supposed to be expelled forward from the water being pushed out by the piston? Also, I have about 2 meters of line on this gun, can it get deformed at the end of the line from the remaining energy of a missed shot?
I have no explanation how and why his happened. Any ideas?

P.S. I measured the washer internal diameter and I confirm that Seac uses the same washer both for the 7mm and 6.5mm shafts. As a result there is quite a bit of play when used with the thinner 6.5mm shaft.

Deformed shaft butt piece compared to a new one:

 

[popgun pete]

Hmm, that deformation should not happen as usually the stop ring gets slightly stretched and tends to jam on the shaft stop after a number of hits. To hammer up the metal shaft tail instead is rather bad. The spear tail collects the stop ring in the muzzle as the shooting line and slider hold it back in the muzzle entrance where the stop ring sits. That is where the major impact is as the spear hits maximum velocity and sends the stop ring up to that velocity in an instant. I measured my Shotgun 90 shaft at 103 cm length and 6.5 mm diameter, but being a Hawaiian or integral tip shaft it is not of much use to me. Unfortunately most pneumatic guns come with such shafts these days because they are cheaper than supplying a threaded end shaft and screw on tip. You should send that photo to Seac Sub and register a complaint.

 

[popgun pete]

I plan to buy a threaded end 7 mm shaft for the gun, I don't care much for 6.5 mm as where I spear the fish require drilling with something heavier. Although plenty of European spearfishing uses this smaller size as fish stocks must be more whittled down in the Mediterranean.

I would guess that the lip of the unscrewed spear tail is too thin in section and made of soft stuff, but why has this problem not been observed before? Need to check how many other Seac-Sub models use this skinny shaft.

 

[popgun pete]

The Seac-Sub 2020 catalog is now available and here is the page entry that shows their pneumatic speargun shafts. Only Asso 13mm and Caccia HF 11.2 mm pneumatic gun models are listed, looks like the other models have now been dropped. Remember that the screw on speartip adds to the length of the shaft, the sizes in the table are the shafts as depicted below with no tip fitted.

 

[Xape]

Yes, could be that the front section was machined too thin out of spec. Will try to unscrew this piece from a new spear end and measure it. These are hard to unscrew, I thought the end piece is press fitted, but no they are threaded.
Thanks Pete for the catalog link, I see Seac had come up with new part numbers... again.
I researched the shaft length confusion I talked in my earlier post:
The screenshots below are from the Seac 2015 catalog.The Shotgun 90 is supposed to come with a thaitian 6.5mm 87.3mm long shaft.
On the shaft options page the available 6.5mm dia. lengths are 88, 100 and 125cm.
It is logical to think that the gun would come with the 88cm, but no - it actually comes with the 1320004/100cm shaft.

The threaded tip shafts are spec'd based on the gun they are supposed to go with, not the actual length. So the 285/B will most likely be 87.3mm long and the right threaded shaft option for the Shotgun 90.

 

[popgun pete]

Well in the latest 2020 catalog the "Shotgun" is not listed and from memory it was not in the 2019 catalog either. Generally the next year's catalogues come out in the latter part of the preceding year. The "Shotgun" spear appears to be spring stainless steel, whereas the pneumatic gun spears in 2020 will be either inox or carbon steel with a protective coating. In the distant past such spears were always cadmium plated, but as rather nasty chemicals are used in that process it has long been discontinued. A 7 mm shaft will make the gun even more nose heavy than with the 6.5 mm original (such a light shaft seems odd in a gun with the name of "Shotgun", however the name is just a reference to its looks as I mentioned in an earlier post).

A cruiser shotgun is most likely if you check out this Mossberg used by the Police.
The "Caccia HF" will only be available in sizes 75, 90 and 115 cm, these guns being the same as the "Shotgun", but with a full length hydroformed tank.

 

[Xape]

One more odd thing I just discovered about the different Seac shafts - Last year I bought two original Seac 284/B shafts to use on my Caccia 65. Now I discover that these have a smaller washer outer diameter. All my other Seac shafts have a 13.5mm washer, while these have a 10.9mm wather. As a result they wobble in the muzzle.

I don't know how this is since all the Caccia's have the same muzzle part Number according to the service manual...

 

[popgun pete]

A stuff up in the supply process or possibly cost cutting. Reduce the weight of anything that you make in the thousands and it can add up over a large production run. They shipped me a “Shotgun” with the plastic power regulator knob busted into two pieces which fell out of the supplied carry bag when I shook it. Took some months to replace the regulator knob and lever as I told them I could swap it over myself being very familiar with dismantling pneumatic spearguns of all types. Could not go to the factory direct, I tried, but had to go via the seller who then contacted the factory so once everyone knew what was going on they sent me two new power regulator knob components. Don’t drop your gun as if by chance they hit a hard surface first those squared knobs will split in two.

 

[popgun pete]

Possibly for the price of a new nose cone and a longer tank you could convert the "Shotgun" to a "Caccia" as that is pretty much what Seac-Sub did. The cylindrical tank rather than the hydroformed tank as I think that the latter are a waste of time unless they significantly bulge the tank for better volume as they do with the "Pelengas".

After eliminating common parts, note that barrels are the same bar the extra grooves for the small "O" rings.

 

[popgun pete]

Just looking at my somewhat unloved Shotgun 90 cm with its itty bitty 6.5 mm diameter shaft it occurs to me you can get some buoyancy back into the gun by adding a buoyancy collar on the skinny front barrel. Those swimming pool noodles are a closed cell foam and have a 20 mm diameter hole down the middle and that stuff can be cut with a sharp knife just like slicing bread. You could fit one long part or a series of rings of this stuff to adjust the buoyancy and more beneficially use a larger diametric shaft like the one in the Caccia gun. As the market didn't like these Shotguns they were dropped. but some were bought at absolute bargain prices and any gun is better than no gun. Have used this plastic foam stuff on my Black Sea gun, but it was a waste of time as that gun is too heavy even with buoyancy collars to float. Aiming and shooting is not a problem as the point of balance is just in front of the grip, but the Shotgun would really benefit from some up front barrel flotation support.

 

[popgun pete]

Buoyance was similarly added to the SOS "Ringo", although those guns were never floaters due to the metal drum that confined the spread of the polyurethane Vulkollan bladder.