It is pretty clear now that Mares treed themselves when they put the Bazooka out. The Titan guns were a means to increase tank capacity of the classic layout pneumatic guns by adding more tank volume forwards of the grip handle. More tank volume, lower compression ratio, higher start pressures and thus more powerful shots can then result. As Mares had all the component parts they just had to use longer tubing lengths to create a range of gun sizes. Once they decided to lengthen the Titan, which was already a sinker, they had to put as much tank length out front as out the back, hence you get this monster, in order to provide a fore-aft balance. But what are you going to shoot with it and the only answer back then was big resident reef fish that for most intents and purposes were armour plated. To make a hole in them that hit something vital you were going to need shaft momentum at the target and that meant a big shaft. Now Classic layout rear tank guns often shot 9 mm shafts, but big fish had been known to just shrug those off with no apparent effect, so the next step up is 10 mm diameter shafts. When you introduce a long 10 mm shaft into the muzzle, and unlike an octopus you only have two arms and two legs, there will be a moment when that big shaft tries to twist the nose off the gun as there is no help from the water displacement up-thrust. Once Mares engineered for shooting long 10 mm shafts the die was cast, but why they resorted to a long stroke shock absorber is hard to fathom. A standard rubber sleeve shock absorber anvil may move a millimetre or so forward when hit by the fast moving piston, but a spring will collapse even more, and you don't want the front piston seal subsequently escaping the inner barrel bore or whoosh and all your compressed air is gone.
We know Mares made rear handle Stens up to 150 cm, but they don't have coil spring shock absorbers and their muzzle look like the usual Sten types, so it is that 10 mm shaft that decides things. Sten guns only shoot 8 mm diameter shafts because the shaft tail stop is sized at 9 mm and that has to pass through the hole in the shock absorber anvil body.
Those with long memories will remember that the big 2 metre long spring guns shot 10 mm shafts, and sometimes larger, but those shafts were hollow, they are not solid steel. The reason for the large shaft OD was the shaft was pushed down a barrel bore of that diameter, actually it was slightly larger, as was the coil propulsion spring, and they didn't want the shaft to rattle from side to side in the barrel tube.
