Hiya
My RA's spear sit also just above the track. How-ever, this changes once the gun is loaded. The loaded band pins the shaft to the track.
Here's some very useful information from the RA Website (
http://www.roballen.co.za/homeset.html )
What's the difference between a Rob Allen Railgun and a basic gun?
Railguns are unique in the sense that they have an extended "rail" incorporated into the aluminum barrel all the way along. This rail supports the spear the full length of the barrel and continues on into the muzzle. The rail barrel tube is also much stiffer and stronger than a normal tube because it is thicker-walled and has a slightly bigger diameter. The integrated rail adds further strength. We also use aircraft grade aluminum when the barrels are extruded. This gives the barrel even better strength and stiffness, enabling it to handle strong rubbers and be used in longer lengths without flexing. It is basically stronger and stiffer than wood of the same diameter
Why is the spear in a railgun shorter than in a standard gun?
The support given by the rail allows the gun to use a shorter spear than a normal gun. To make a standard gun accurate, the length of spear has to be such that the section protruding from the muzzle will counter the sag in the middle section. This will be apparent when too short a spear is used, because it will shoot high. The opposite is true if too long a spear is used, as it will shoot low.
Why can't I put a support for the spear on the barrel and achieve the same result as a rail?
With supports on the barrel the spear tends to drop out of the mechanism when fired and "bump" over the support, causing an exaggerated wobble on the spear. This wobble will slow the spear down a great deal while it is travelling. With a rail this wobble is eliminated totally because the spear is supported all the way along and does not have a sag at the end because it is shorter than normal.
Why does my railgun seem to shoot the spear much faster and straighter than my standard gun?
On a railgun there is no sag in the middle of the spear because of the rail supporting it, and the length protruding out of the muzzle need only be short, therefore the spear weighs less. The drive ratio of the rubber is now much improved because the length relation of barrel to spear has increased; therefore more speed is attained without increasing the rubber strength. Another reason the spear is faster is because the spear does not wobble because it is supported level before being fired, and remains straight once momentum is achieved. Wobbling of a spear develops with a standard gun when the spear has a slight sag in the middle along with sag at the end. The moment the trigger is released the spear tends to "buck" creating a wobble when fired from a standard gun. This obviously creates more friction and therefore slows the spear down a great deal.
Does the spear resting on the rail not cause friction on the spear and slow it down?
When in the water the rail and spear are both wet. Once the spear gets going it will slide on a thin film of water, which eliminates the possibility of it touching the barrel. A well-used railgun shows no wear in the rail, which it would show if there was significant contact friction. This is similar to the way that a slipper bearing or a beach skimboard work.
That should cover the basics on rails on spearguns!!
Regards
miles