Mares Bazooka

[popgun pete]

Looking into the black anodized alloy nose cone.

I had to hold the gun up and simultaneously lean back to get some sunlight to illuminate it without falling over to take the above shot, the Bazooka is a very heavy gun. Again all black inside and the inner barrel which looks black will be coated with some anti-seize compound. In the old days this was some thin white stuff with a slight blue tinge, apparently now replaced with something else, or at least when this one was manufactured. Just when it may be possible to work out from the serial number, but I expect many of the Bazooka guns sat in stores a long time before they were sold.

 

[popgun pete]

Note it is possible to have all four relief ports exposed, but if you do the muzzle up tight as they had done at the factory and depending where the holes are with respect to how the screw thread was cut then they end up being on this gun in a cross form rather than a X. What you should do is tighten the thread up, then back the muzzle off by a fraction of a turn to get the ports in the correct position. Pressurizing the gun then pushes the nose cone forwards, thus jamming the muzzle in the right orientation. In fact you can do this on any gun, but most don't worry about the relief port orientation, however on the Bazooka you need to due to the vertical slots on either the side of the nose cone allowing water to jet out with the shot. Otherwise you get a form of hydro-braking in the gun, some occurring anyway due to the small relief ports, smaller than they are on the contemporary Sten!

 

[popgun pete]

Just to add some perspective to the sizes involved. The top spanner was required to budge the Bazooka muzzle without damaging the anodized finish of the parts.

 

[ARL58]

You do an amazing job analyzing these spearguns! I think that nobody but the maintenance guys at the time were so knowledgeable. Some great spearo's from the past used Bazooka a lot: Massimo Scarpati and Romano Perotto among them. both still with us and present on Facebook .

 

[popgun pete]

You do an amazing job analyzing these spearguns! I think that nobody but the maintenance guys at the time were so knowledgeable. Some great spearo's from the past used Bazooka a lot: Massimo Scarpati and Romano Perotto among them. both still with us and present on Facebook .

Well thanks, but the Bazooka is really a gun for a certain type of job, you would not use one for general spearfishing. Same for the Alcedo Hydra, they were just used for shooting big fish as well. The advantage of the Hydra was purely in loading it, you could break the task into small sections and when they added the knitting needle plunger displacement hydropump nearly anyone could load it, although it took some time to do. The world is a much different place now, underwater TV shows what swims in the deeper water, when in the distant part unless you dragged the big fish out no one would believe you. Only when the jib on the pier crane nearly buckled did people realise what was down there, but unfortunately everyone then overdid it and the big fish, easily reached ones that is, were decimated. Now those fish, which have since recovered in numbers, are off limits.

 

[popgun pete]

With the muzzle loosened the air pressure assist method can be used to push the nose cone out, the problem now is to operate the Mares hand pump on a 140 cm long gun as you cannot do it just standing up. Looks like a set of steps is needed.

 

[popgun pete]

As it turned out the Bazooka hand pump doesn't work, possibly the seal has dried out on the pumping piston nose and shrunk, but having tipped oil into it the pump hasn't worked so far. This hand pump is not the one usually sold with the gun, all the early Mares hand pumps had cylindrical handles and bayonet quarter twist connectors that go in the matching rear end of the inlet valve body. Mares put Tee handles on their later hand pumps and they also have screw threaded nose fittings. So that the old timers were not left stranded Mares offered end adaptors to convert the new pumps. On this Bazooka Tee handle hand pump someone has screwed an adaptor for the bayonet type fitting into the pump body and probably it was Mares themselves. Pretty sure that these late model Bazookas were assembled from remaining stock of parts because they were still selling them after all the other Titan models had been discontinued, having been killed off by the Stens.

I have quite a few bayonet connection hand pumps, so will be using the one for my Mirage, it also has a bayonet fitting. The Mirage is in pieces again, so its pump doesn't get much use.

 

[popgun pete]

Here are some photos of the Mares hand pumps. Since I last wrote the Bazooka pump has come good after pulling oil up into it and leaving it for a couple of days. Note in the old tubular handle Mares pumps you can undo the rear nut and pull the pump rod out. No such easy removal of the pump rod in the later pumps as the retaining element is a round bush. The quarter twist bayonet connection to the gun was very convenient, but they have a larger dead space which only becomes apparent when you are facing around 1000 pump strokes into the gun. That puff of lost air as you pull the pump rod back costs you more pump strokes for the same pressure with the threaded nose pump.

 

[popgun pete]

The reason for the larger dead space in the quarter twist bayonet connections is when pressure builds up at the entrance to the gun's inlet valve the pressure blows the pump back against the locating lugs and moves the pump nose "O" ring slightly further back in the locating bore in the gun's inlet valve body. By way of contrast the same "O" ring pushing into that bore cannot move with the newer model pump because it is held there by the screw threads on the pump nose. Ideally if you have older guns you can swap out the inlet valve body for a new one using screw threads for the commnction, the most difficult aspect is obtaining the new inlet valve body. Then the number of pump strokes on big interior volume guns will be reduced for the same pressure level being obtained in the gun.

You can see this in the Mirage table above, the older gun in 80 cm, there was only the one size sold (blue table) had a quarter twist bayonet connection, the later 80 cm and 100 cm Mirage guns (white table) had a screw in hand pump.

Thus to get the 80 cm gun to 40 bar it required 1100 pump strokes with the bayonet twist hand pump and only 680 strokes with the screw in pump. Seems a big difference, but that is because dead space losses hold a lot more air as the pressure goes up. You are not quite going backwards near 40 bar, but you can see that you are losing lots of air as you pull the pump handle back and you then have to recompress that air again to refill the dead space to 40 bar before the inlet valve opens to admit air into the gun.

Transfer these pump connection losses into the mighty big tank on the Bazooka and you could be there for hours pumping it up, if not days.

 

[popgun pete]

A rare hot day, I unscrewed the Bazooka muzzle for about three turns and then put about 15 pump strokes into the gun. So that all interior spaces in the gun are connected the power regulator is set to full power, this guarantees no surprises when letting air out again.

 

[popgun pete]

With the gun under enough internal pressure to push the nose cone out and yet not so much that the muzzle will not budge when turning it by hand the process begins.

 

[popgun pete]

When the nose cone looked about half way out I released all the air from the gun and then twisted the nose cone out by unscrewing it as it did not want to pull straight out for some reason, could be a close fit of its inner bore on the inner barrel nose end threads used to attach the separate muzzle. After the nose cone was removed I pulled the piston out. The piston is a three seal piston with an annular plastic bush, so it has everything.

Note the crack in the grey plastic bush is how they fit it onto the metal piston. This allows it to be sprung open slightly to pass it over the piston nose and then slide it into position in a recess cut in the piston body for that purpose. These bushes are intended to stop the piston wobbling in the barrel bore by being a closer fit in the barrel. With the 11 mm tail stop diameter on a 10 mm diameter shaft you don't want lateral movement when the barrel bore is only 13 mm, that is down to a clearance of 1 mm on either side! Compare this with a stop diameter of 9 mm on an 8 mm shaft in a 13 mm barrel or 8 mm on a 7 mm shaft in an 11 mm barrel. No wonder then that they put a much longer piston in the Bazooka!

When plastic pistons arrived they in a sense made the entire piston body an aligning bush in the barrel bore, that defeated piston wobbling, but get sand grains embedded or jammed in the plastic piston and that was the end of your inner barrel bore's smooth surface finish as they cut through the anodizing.

This is the reason why Russian and Ukrainian pneumatic spearguns usually have stainless steel inner barrels due to more gritty water conditions in rivers and lakes.

 

[popgun pete]

With the nose cone and piston removed I upended the gun with its front end in a clean glass jar in order to drain all the oil out. It will take some time to get out of the brass cup pre-chamber in the tail end of the gun as the only way out is the power selector piston plug which with the gun set at full power is pulled right back from the transfer port in the partitioning bulkhead.

 

[popgun pete]

I will not try to pull the outer cylindrical tanks off yet as I want virtually all the oil out and I don't want dust blowing on the exposed innards of the gun so will probably do that work inside. The Bazooka is the biggest full length concentric tank gun I have ever worked on, but it is not the biggest speargun I have worked on.

The Alcedo Hydra is even longer and heavier, both versions, including the Sprint 62.

 

[popgun pete]

While the front end of the gun is opened up I have covered it with a plastic tumbler as seen here.

These are views of the open tank end. You can see the black coating on the inner barrel nose thread and inside the tank the silvery object is the circlip on the inner barrel that holds the plastic bush that the "O" ring presses against in order to seal off the nose cone and muzzle when these items are installed.

Note the thickness of the tank walls, one of the reasons the gun is very heavy. The wall thickness is not for pressure retention, it is to stop the gun being dented if it ever hits the bottom as these guns do not float after the shot. No Classic layout gun ever did and essentially the Bazooka is one of those, but the Titan series were developed to have an extra air tank in front of the mid-handle and they eventually extended it right through to the muzzle. The benefit of a long air tank was a reduced compression ratio that allowed higher start pressures in the gun. No one seemed to think about actually muzzle loading it.

In the days of spring guns and very early almost monotube pneumatics the start of loading effort was not that great and progressively increased as the shaft was forced into the gun. Low start pressure, high compression ratio pneumatic guns are not that different from spring guns in that respect. But high start pressure guns that have a flatter pressure growth curve due to their lower compression ratio are going to be a struggle from the beginning, not such a problem if the gun is under a metre long, but extend the gun out to over a metre and a half and things become a lot more difficult, plus you have to hold the Bazooka up in the water column.

A low start pressure, high compression ratio speargun is very similar to the low power shot on a dual power rear handle speargun. All pneumatic spearguns are basically a long tube with an air tank attached at the rear, the tank can be small or large in volume and either extend out the back or be wrapped around the barrel tube in a concentric layout.