F.A.Q. How To Measure Speargun Rubber Size?

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F.A.Q. How To Measure Speargun Rubber Size?

This question depends on four factors: The mass of the gun, the shooter, the diameter of the spear and the mechanism. Let’s look more closely at each of these factors.

The Mass of the Gun

The gun must have the appropriate mass to handle the recoil of the discharge. A common problem with in-experienced divers is to load up the gun in the belief that they can shoot further and secure more fish. If the gun is to light then the recoil produced sharply raises the muzzle as the spear is leaving the mechanism there by kicking the rear of the spear up sending it in a downward trajectory. This results in a shot that is low and the inexperienced diver falsely thinking that he needs more power.

The Shooter

Divers vary in their ability to handle recoil both with technique and their individual strength. A gun that is one spearos dream can easily be another spearos worst nightmare.

The Diameter of the Spear

The diameter of the spear is the determining factor here because a steel spear does not behave it’s self like a spinning bullet leaving a riffle. A spear wanders through the water once released. This is due to the elastic nature of the steel used to construct the shaft. A thin spear will lose control. When the trigger is squeezed the power bands come into action and apply an enormous accelerative force to the spear. This sudden acceleration combined with the spears natural inertia and elasticity causes the spear to hump up and jump as the back of the spear try’s to catch up to the front. As the spear flies this humping effect creates an oscillation or wobble in the spear and it snakes through the trajectory. You can observe the results of this oscillation on a well used rail gun, there are scuff marks at regular intervals along the rail where the spear bounced through.

The Type of Mechanism

The type of mechanism is a question of safety. All guns that accept a European shaft, (a shaft with a rounded cut) should not be loaded with more than two 16mm power bands. This type of mechanism works on a slip principle, i.e. the spear slips of the sear when the trigger is depressed. Do not listen to any one or any advertisement that tells you different.

So what does all of this mean for you?

The length and diameter of your speargun rubbers will definitely affect the overall power of your speargun. In addition this can have flow on affects for the range and accuracy of your speargun.If you have a 90cm speargun for instance then a rubber measuring 50cm with a 16mm diameter will provide you with a standard, medium strength power ideal for reef and wreck fishing.If you are hunting for larger fish then you can decrease the length of the rubber to 45cm.This will mean that the rubber has to be put under more tension to stretch it along the length of the barrel and this will increase the power of the shot. This can result in additional penetration power for your spearhead for larger fish species.

The following is a recommendation only and are the lengths that work best for an all round power ratio. Shorter lengths will give additional power however be careful not to overpower a gun as this will decrease accuracy and make re-loading harder.


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