We have already had nice slim airguns, Technisub made the "Jeans" and "Grinta" guns that had 30 mm diameter air tanks, otherwise they were similar to the usual rear handle guns (most of which now have 40 mm diameter air tanks). Of course they never floated after shooting them, due to insufficient water displacement for their weight, even though the guns were relatively light. A higher compression ratio (less air tank volume) meant that they were not as powerful as the fatter tank guns like the "Sten".
If you superimpose the rear of your pneumatic gun over your target while long shot sighting and it is in the linear trajectory shooting zone then you will hit your target where you aim at it (provided the shaft is nice and straight). For tracking "from the hip" shots you are mentally intersecting the axial line of the gun and tip with your direct visual eyeline on the fish, you can see where the tip is pointing because the gun is angled towards the target and viewed from the side. When the convergent lines look about right your brain automatically pulls the trigger as success comes from long term practice, especially with using the same gun.
Actually the pneumatic guns that we have today are the product of an evolution that has gone through the designs that you are talking about, it is not that manufacturers are not thinking outside the square, they have already been there. Why most guns look like variations on the "Sten" is that the other designs could not compete in terms of their construction costs and the light weight of a gun that can still use up to 40 atm of air pressure. All the early pneumatic spearguns were home-made, so if you really want something like this separate barrel gun then you either have to make it yourself or get someone to make if for you. The barrel has to be well secured to the tank lest it be torn off during gun handling, so it needs to be a rugged construction.
In Russia and the Ukraine there is a long tradition of speargun "gunsmithing", classed as "home-made" guns, which rival the factory production guns made over there (a cynic may say that would not be too difficult due to the often chequered history of the latter!). So if you want a "barrel on top" model made try looking over there, however the "evolutionary wheel" is at work there too and their own guns are starting to look very much like our guns.
If you superimpose the rear of your pneumatic gun over your target while long shot sighting and it is in the linear trajectory shooting zone then you will hit your target where you aim at it (provided the shaft is nice and straight). For tracking "from the hip" shots you are mentally intersecting the axial line of the gun and tip with your direct visual eyeline on the fish, you can see where the tip is pointing because the gun is angled towards the target and viewed from the side. When the convergent lines look about right your brain automatically pulls the trigger as success comes from long term practice, especially with using the same gun.
Actually the pneumatic guns that we have today are the product of an evolution that has gone through the designs that you are talking about, it is not that manufacturers are not thinking outside the square, they have already been there. Why most guns look like variations on the "Sten" is that the other designs could not compete in terms of their construction costs and the light weight of a gun that can still use up to 40 atm of air pressure. All the early pneumatic spearguns were home-made, so if you really want something like this separate barrel gun then you either have to make it yourself or get someone to make if for you. The barrel has to be well secured to the tank lest it be torn off during gun handling, so it needs to be a rugged construction.
In Russia and the Ukraine there is a long tradition of speargun "gunsmithing", classed as "home-made" guns, which rival the factory production guns made over there (a cynic may say that would not be too difficult due to the often chequered history of the latter!). So if you want a "barrel on top" model made try looking over there, however the "evolutionary wheel" is at work there too and their own guns are starting to look very much like our guns.
