The growth in spearfishing and the different techniques divers now use to stalk their prey nowadays has created the need for lighter, more maneuverable, faster and more quiet weapons. So let’s look at all the different factors that influence a speargun.

The starting point to judge a band gun is its balance. Many divers make the mistake of unbalancing their guns by adding power to it without even having tried it, unknowingly this results in disadvantages instead of the benefits they seek. Overpowering a gun almost always causes a decrease in precision and an uncomfortable shot. Many divers who make these changes do so in the hope of shooting a big fish, but they will loose plenty of chances to land smaller fish as a result of poor accuracy. And this, without having any certainty of running across the big fish they sought. A capture of a nice fish is very much a reality with a standard weapon without having to have a cannon. Increasing the power of the bands, three negative effects are usually achieved: the first is usually a decrease in the sensitivity of the trigger mechanism, the second is a whiplash effect because of the increased power which acts negatively on the gun usually moving it somewhat, the third is dictated by the lack of balance between the forward pushing force of the bands and the weight of the shaft, the opposing force. Let’s analyze them better:

The sensitivity of the trigger mechanism is very important. When a trigger mechanism becomes too hard you risk shifting the entire spear gun trying to pull the trigger. If it’s very sensitive you have the advantage of only having to make a small traction with your finger to release the shaft. With a sensitive trigger the weapon stays pointed firmly at the target whereas with a hard trigger invariably it shifts if even slightly. That minimal movement in the tip of the speargun can change the aim as much as several inches on the final target depending on the distance. In fire arms, especially hand guns, the firing mechanism is fairly sensitive. In spearguns a compromise of a medium sensitive trigger mechanism is okay because the stability of the weapon in the water allows an efficient traction on the trigger for a precise shot. It can’t be too stiff however as it will cause it to lift and shift.

The best rule of thumb therefore is that pulling the trigger shouldn’t have an effect on the movement of the gun.

The relationship between bands and shafts is fairly comparable to a javelin thrower and the javelin. Take a strong javelin thrower and give him a javelin that is too thin and during the launch it will vibrate consistently until it falls short because it lost a lot of energy although it had plenty of power behind it. And vice versa if you take a javelin that’s too heavy for the thrower it will only go a short distance without the power to launch it efficiently. With a lance of the ideal weight for the javelin thrower, once its launched there aren’t vibrations and loss of energy allowing it to carry its flight efficiently and streamlined making the most of the javelin thrower’s power. This is the desired combination we seek with spearguns as well.
Shafts that are too light with bands that are too powerful waste energy without maintaining the desired direction. Shafts that are too heavy with bands that are too weak don’t maintain a constant direction falling short of the target. Guns with an ideal balance between power bands and shaft result in perfect shots.
There are many types of bands and spear shafts with different strengths and thickness from different producers so it’s not safe to make exact judgement about the relationships between each of them. Generally as a rule of thumb however we know 6mm or ¼” shafts are ideal with a 16mm bands, and 6.5 or 7mm shafts are a good match for 18mm or 20mm bands. If we decide to use double bands, 6mm shafts should be avoided.

As usually is the case there are differences of opinions on the subject but since logic is not an opinion, divers who get used to different variations from these general rules of thumb and swear by them are wasting the opportunity to make the best of the power and accuracy of their gun.

One consideration that should always be kept in mind is the aerodynamics of a spear shaft and its flight. It could be bent causing it to shoot off target, just as the barb could be too big or not aerodynamic for the shaft, as well as the possibility of the shooting line being too thick, factors that all could possibly lead to a bad shot. Even the type of steel used for the shaft plays an important role. A soft type of steel can be influenced by the power of the push of strong power bands. The pressure will cause the shaft to flex which should straighten it self as soon as it leaves the gun. A soft steel doesn’t have the right memory to return to its original shape fast enough. A more “springy” steel suffers less from this problem bending less from the traction of the rubbers springing back to its shape immediately. For these motives a harder grade spring steel is much preferable to a soft grade.

The shooting line. Most commonly a good all around shooting line is 300-400lb test, between 1.6-2mm which has the combination of great breaking strength as well as fairly low friction in the water following the trail of the shaft. Naturally the smaller the shooting line the less it influences the accuracy during the shot which is why anything over 400lb test on a band gun with a 7mm or thinner shaft is overkill.

Lastly, understanding the particulars of a speargun and its workings is important but we should never forget that the best thing is going diving as often as possible and there’s no substitute to learn how to shoot a fish. Figuring out one’s personal habits will just help determine what speargun is more ideal.