Like many of us who encountered the problem of choosing underwater hunting arms, I could not find a worthy specimen among factory-made models or products of experts - do-it-yourselfers, which would satisfy my needs in full. All products, offered by more than ten manufacturers and represented by over one hundred and fifty models of underwater guns, had in my opinion a number of shortcomings which could completely neutralize all their qualities. Best is the enemy of the good; and I set to work.

It all started

At first I attempted to manufacture all guns from scratch, so to say.
For this I used all the best elements of structures applied in existing designs and created a certain averaged vision of an “ideal” gun. Surely the gun was pneumatic, with sear trigger mechanism (no valving), stainless steel 12 mm barrel, a pistol grip with integrated bobbin in the middle or at 1/3 from the rear cover, receiver material – surely 36-40 mm titanium. Harpoon – 8 mm, piston – combined: caprolactan, chisel stainless steel.
Everything would be great, but I wanted to shoot farther and more accurately, without toss-up which is inherent in practically all guns with a grip in the middle of the receiver or closer to the gun end. I wanted to shoot quietly, to avoid the typical ringing stroke of the piston on the (отбойник) which would scare all kinds of fish.

All pneumatic guns have one common shortcoming irrespective of the trigger mechanism design, gun maker name etc. This shortcoming is “parasite” water which fills the gap between harpoon diameter and barrel inner diameter in the course of gun loading and limits significantly the harpoon’s maximum initial speed, thus impeding the range and accuracy of hitting. There are different ways of dealing with "parasite" water.

Zelinsky guns manufacturers have discovered, in their opinion, the golden section: 8 mm harpoon and 10 mm piston. Italians designed a gun with 7 mm harpoon and 11 mm piston (MARES Cyrano Stelth), i.e. they minimized the disparity between diameters. BUT! The less the disparity between harpoon and piston diameters, the more the piston and the (отбойник) are subject to emergency deformations. Those whose gun was jammed at least once in the hunting field due to a cracked piston, splintered (отбойник) or piston stuck in the (отбойник) will grasp the idea. The solution is to produce the piston and (отбойник) from alloyed chisel steel; however the gun report is unforgettable. There is another, more radical solution: to prevent “parasite” water from penetrating the barrel. This principle of pneumatic gun design is called “pneumatic gun with dry barrel”, or “pneumovacuum”. The idea is not a new one. It emerged and was successfully brought to life in the early 80s of the previous century. Dnipropetrovsk underwater hunting enthusiasts, e.g. Pavel Sergeyevich Semenyak (presently founder of Andreyevskiy SMAK Underwater Hunters Club in Dnipropetrovsk), made great progress in this direction. “Pneumovacuum” provides a designer with multiple ways of realization but requires a completely different approach to the materials choice for the piston and, of course, steels for the slide bushing and (тыльник). The harpoon ought to be of high quality as well. In theory the piston can be of any diameter, allowing production of “perpetual” guns with a “non-destroyable” piston and (отбойник). The diagram of a pneumatic vacuum gun for underwater hunting is presented below. As shown in the diagram, the basic element distinguishing a pneumatic vacuum gun from the pneumatic gun is a vacuum cuff (dispensable element) which prevents water from penetrating into the barrel hollow in the course of gun loading, hence the absence of nozzles, needless in this situation, generally employed for that “parasite water” discharge. The main advantages are evident:

а) the piston moves in a vacuum medium which tends towards compression, giving the piston an additional impulse, contrary to incompressible water slowing down the piston. In practice this promotes a significant increase of the harpoon initial speed, with all other conditions remaining at the same level. As a result of the foregoing, you do not need to pump your pneumatic vacuum gun excessively, which permits manual loading of the harpoon and eliminates the necessity to use a loading device. Toss-up in the course of shooting is also reduced

b) absence of nozzles for water discharge, which per se reduces shot noiseness in comparison with the pneumatic analogue (provided that the (отбойник) is redesigned in a certain way, the following result can be obtained: a shot is practically inaudible in the water at a 8 m distance)

c) the harpoon is supported in the barrel by vacuum, i.e. it is possible to eliminate the Morse cone, located on the harpoon (тыльник) and used for harpoon holdback in the piston, from the gun design. This structural component “steals” from 2% to 5% of the shot energy, depending on the wear degree and structural peculiarities.

d) the harpoon may be of any diameter. The following diameters are used: 5.7 mm, 6.32 mm, 6.5 mm, 7 mm, 8 mm. Light harpoons (with up to 6.5 mm diameter) demonstrate very high initial speed, produce practically no toss-up and are used for shooting quick fish, e.g. mullet and Mugil soiuy (no adjustment with regard to movement is required). 7 mm and, the more so, 8 mm guns have greater penetrating power and are used for large fish shooting. Depending on the expected trophy during the forthcoming hunting, a harpoon most suitable in terms of diameter can be attached to the gun. Replacement will take several minutes.

MARES Cyrano 970, adapted for vacuum, with harpoon diameter 6.32 mm, approved itself in point shooting at a 6-7 m distance at mullets of 400 – 500 g. The next step for guns improvement is transition to stainless barrels (GURZA project). This will permit to minimize the friction coefficient of the barrel and piston unit from 0.25 to 0.01. The practice of barrel replacement demonstrated that, under other equal conditions, guns with 10 mm stainless steel barrel have the maximum efficiency. There are practically no factory-made or do-it-yourself pneumatic guns which cannot be modernized in a similar manner. The greater the disparity between the barrel inner diameter and the harpoon, the more justified is the usage of vacuum.