Rene Salles invented and patented in 1946 the first pneumatic speargun with a trigger mechanism built into the gun rather than having an external mechanism using the forward latching system. This involved what was essentially a single-piece trigger that was pivoted on one side of the gun in what we would call an "outrigger trigger". This design enabled the pressurized section of the gun to be penetrated by the trigger pivot pin which crossed the gun's pressure boundary. Thus it could be regarded as the first pneumatic gun from which all our current guns descend where a sliding piston with a mushroom tail is held back by a sear tooth located inside the gun which is released when we pull the trigger.
Rene Salles manufactured a number of different models as can be seen by this advert from 1965. Basically the layout did not change much from his original 1946 design, but subsequent models were produced in lighter versions to reduce the overall weight of the guns and as part of this reduction the built-in hand pumps weight was reduced. The pump handle was a big lump of metal at the rear which also served as a counter balance to the forward barrel and spear, thus the weighted end was reduced for the guns that shot lighter spears of a smaller diameter. Pistol versions being short did dispense with the rear weight as then it was not required. Note that the spear in all these guns only occupies the front barrel as the sear lever was located in the grip handle, a feature which was shared by the later Nemrod pneumatic guns from Spain. These early pneumatic guns were often slow leakers as a consequence of how they were constructed with press fits and rubber packings and washers which were not 100% effective. The dynamic piston seals were made from oiled leather following the practice of dynamic seals in automotive brake and suspension applications. Back in those early days "O” rings were yet to be invented and plastics were hard brittle types like “Bakelite” which were only suitable for reel drums.
The above Salles "Le Pneumatic" gun is one of the lighter versions, however all these guns were sinkers after the shot and this was not considered a drawback as their main opposition was the spring gun which sunk like a stone when dropped. Band guns had poor rubber initially and were no match for the big spring guns that had been around before the Second World War, but in the following decade this was to change rapidly as the band gun outsold everything else and were compact when required. These early pneumatic guns followed the path of the spring guns flinging spears from 11 mm and down to 9 mm diameter, so heavy shafts were the order of the day.
The "Normale" gun was the big banger and was available in 3 lengths and is basically the original 1946 gun as shown below. These guns had the hand pump incorporated into the rear tank and as can be judged by their overall dimensions were low start pressure, high compression ratio spearguns.