- by Rob Allen
Rob Allen’s slip tubes are designed to shoot small groupings in the area where the average person would instinctively point. This is only the first half of the equation – the human factor is as important. We have found normal slip tips are rarely accurate as the tip normally has a little play. This, being right at the tip is where is has the most adverse effect. With the slip tube, the spear becomes the point, greatly improving the control of the spear.
Other factors that can cause inaccuracies come from the gun itself. What will change the point of aim and grouping is the stiffness of the barrel (obviously predetermined), the tightness of the mechanism fixing in the barrel, the stiffness of the mechanism (trigger pull), mass of spear and gun, length and straightness of the spear, and the tension in the band or bands (with the slip tube it is better to increase the rubber load a little as there is more drag from the cable and crimps). The accuracy can also vary pending which hand the gun is held in.
The main factors from the users point of view that will affect the way the gun will shoot, are your basic athletic abilities, the strength of your shooting arm, the way you grip the gun and, how you aim (sight). You might be lucky and your own make-up will complement the setup of a gun you buy. It is always best to spend a little time target shooting in a pool to develop an awareness of the way you shoot and perhaps some minor tweaking of the gun will result in a big improvement in your accuracy.
When shooting and or testing a gun with a slip tip, always hold the gun out with the arm extended and as stiff as possible. Make sure you always wrap the line the same way each time to maintain consistency. It is very important to set the tube up such that all the cable is on top of the tube (see picture) Set the cable up with the trailing section tucked into the middle muzzle hole (with the spear). If you are using an open muzzle, trap the cable under the mono when wrapping it around the spear. The best method to adjust where the gun shoots in the vertical plane is by the two trailing barbs on the slip tip. These trailing edges can be bent up or down depending where you need the shot placed. This edge acts like a small aerofoil. An adjustment of about 1/2mm on the barbs trailing edge will make about a 50mm change at max range compared to before the adjustment. It is good to test your gun and adjust accordingly each time you change the spear and or the rubbers. If the spear shoots low, flatten the top trailing barb a little and open the bottom one a little then test. The reverse is true if it shoots high.
Your spear placement will change over time, as the rubbers get old. When you replace the old rubbers there will be a variance from the old to the new. The tighter the rubber the quicker the spear will get to the target and therefore the less the drop due to the arc of trajectory. Rubbers also vary a little from make and from batch to batch. To recap, if a gun with a slip tube shoots high, flatten the barb underneath and open out the top barb a little, if it shoots low, do the opposite.
There will also be a slight left to right deflection pending how strong the gun is set up and how tight you hold the handle. This will be more evident with the slip tube. Also, if the gun is over powered this will be much more noticeable, this is due to the recoil. What happens is that the recoil causes the mechanism to rotate in your hand just a little but enough to deflect the spear. A right-handed person will find the gun shooting a little to the left while a left-handed person to the right.
NB: Very important! Do not leave the tube on the spear when not in use as the dissimilar metals will cause corrosion. Keep lubricated when in use.
Click here to view diagram.