Scubamazing, it's called "freediving". We used to call it skin diving, same thing. Yes, it was all about hunting. Scuba came along and the rest is history but spearfishing while freediving remains extremely popular and, in fact, is mandated by law in the Bahamas and much of Europe, etc. The gun is not aimed like a rifle. There is a kind of sighting, but it is done over and above the barrel, what they tell rifle or shotgun shooters to never do. This type of aiming is similar to what archers call "gap shooting". That is, the diver practices with the gun, begins to understand the sight picture and it's relation to the range and speed of the arrow in relation to the target. With rear grip guns, the arm is extended and the diver gets a sense of the arrow and it's travel. The range is proportionate to the power of the rubber bands. If the arrow shows a drop of more than an inch at typical distance to target, then a more powerful gun may be needed. There is a category of divers who use guns without shooting line, called "freeshafters". These people will sometime "lob" a spear at long distance and hope the trajectory will hit the fish. This is similar to artillery ranging. A typical straight line range for a medium size gun with three bands and employing a line is 18 feet. However, the practical range, insuring good penetration, may be less.