Using bulk Rubber

Bulk rubber is a cheap alternative to buying ready made spear gun rubbers, often using higher quality rubber than you can get from the spear gun manufacturers. It also allows you to customize the amount of power you get from each band, and the amount of exertion that is required to load your gun.
Most rubber powered spear guns can be converted to using bulk rubber quite easily. This guide will show you how to perform this.

Types of Bulk Rubber

Commonly there are two types of spear gun rubber - 16mm and 19mm. The difference between the two is the amount of stored energy they can hold. A single 16mm rubber can store less than a 19mm rubber, and as such will require less effort to load. If you are requiring more penetration at long range, you can opt for a 19mm rubber in place of the 16mm, or use multiple bands.

How much rubber will I need?

The easiest way to determine this is to measure your old spear gun rubber. If it was too easy to load or lacked power, shorten it a little. Alternately if you were having problems loading your gun, then make your new rubber a bit longer - you can always shorten it at a later date.

If you do not have your existing rubber, you will have to use the chart below to determine the best length for your new spear gun rubber. This is just a starting point, and will vary slightly with different batches, and manufacturers of rubber. If in doubt, make the rubber longer than required, and shorten it later.

Gun size for these charts are determined by the length of the gun's barrel.

Types of wishbones.

There are a number of different arrangements for spear gun wishbones. These are dependant on the type of spear you are using, and all of these different arrangements are able to be used with bulk rubber. It is suggested that you stick with the same type of wishbone that your gun originally came with. As always there are a few instances where it is possible to use different types of wishbones than those that came with your original rubber.

Please note: These are only a few of the wishbones available for use in bulk rubber.

Bulk rubber replacement wishbone for your gun	Original wishbone for your gun

Constrictor Knot.

This simple knot is the basis of all bulk rubber spear gun bands. It is easy to tie, and provides incredible compression on the rubber. It is best tied with 2mm nylon rope. Any thinner will cut into the rubber, and any thicker will not bind up on itself correctly - allowing for the knot to come undone.

Neatly form the constrictor knot paying close attention to keeping the knot symmetrical.
To achieve the neatest results position the knot close to the end of the rubber, 5mm from rubber edge to knot centre is recommended.
Apply equal pressure to both cord ends to secure the knot. The knot should be tightened to the rubber's maximum constriction.
Trim and seal both ends of the cord with a flame.

Attaching your wishbone to the rubber.

This is the fun part.
For wishbones with metal rods, such as the top two examples in the above table: Simply lubricate the ball ends with dishwashing detergent, and push them 3cm into the hole in the bulk rubber. Once inserted into the rubber, tie a constrictor knot in the end of the rubber - 5mm from the rubber edge. Repeat for the other end , and you're done.

For Dynema and multi-strand wire wishbones, it is recommended that a special insertion tool is used.

It is however possible to use a pair of long nose pliers, and a block of wood to hold the pliers open to perform the same job.
Once the wishbone ball is inserted about 3cm into the rubber, it can be tied off with a constrictor knot 5mm from the edge of the rubber. Repeat for the other end, and you're done.

 

Euro Gun conversion - screw in rubbers

Converting a Euro gun to use bulk rubber is a very simple process. Adapters that screw into the muzzle are all that is required to perform this. They are quite expensive, but bear in mind that these can be used again and again.

Above is an image of a screw in type rubber made up using bulk rubber, and the adapter used to do this. As you can see, the rubber has been tied onto the adapter with a simple constrictor knot.

Buying the fittings.

Most fitting can be purchased from Adrenaline Spearfishing in Australia.