What's the difference between a Rob Allen Railgun and a basic gun?
Would the extra aluminium not increase the barrel weight making it heavy to handle?
Why is the spear in a railgun shorter than in a standard gun?
What are the advantages of a shorter spear than normal?
How does an incorrect length spear affect the accuracy of a standard gun?
Why can't I put a support for the spear on the barrel and achieve the same result as a rail?
Why does my railgun seem to shoot the spear much faster and straighter than my standard gun?
My railgun feels heavier than my standard gun but in the water it is much lighter and more maneuverable. Why?
Why does my standard gun lose accuracy when I fit stronger rubbers?
Is the railgun not noisier than a standard gun because of the spear being against the barrel?
Does the spear resting on the rail not cause friction on the spear and slow it down?
If my spear gets a little bent will it be able to still work in the railgun?
Why do most railguns only use one rubber?
Why is it better to attach the spear line to the back of the spear and not onto a slide?
Is the wishbone notch in the spear not a weak point, considering the fact that the line attachment point is behind the notch?
Why do most divers use monofilament nylon, surely it can cut on the reef easier?
Why do railguns not have screw-on rubbers in the muzzles?
Why are single fixed barbs most common on railguns?
Can a railgun be loaded with the line under the spear?
While the line on top not interfere with the rubber during loading?
I have been using a standard gun for many years and now I find it difficult to aim with a railgun, is it just me or what?
Is a small shock absorber on the shooting line necessary?
What is the advantage of the clip on the muzzle where the spear line is attached?
How do I use two guns at the same time?
Why are plated spears becoming more popular than that of stainless steel?
Why do some divers use bungees (shock absorbers) on their float lines?

 


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.

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Would the extra aluminium not increase the barrel weight making it heavy to handle?

It does increase the barrel's dry weight, but we have increased the internal diameter of the barrel to allow for a greater air cavity, giving the gun more buoyancy, therefore compensating for the extra weight and making it feel light in the water.

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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.

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What are the advantages of a shorter spear than normal?

Having a shorter spear in relation to your barrel length means less drag at the end when swinging the gun onto a fish, improving maneuverability. The shorter spear is also stiffer, and therefore less likely to bend.

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How does an incorrect length spear affect the accuracy of a standard gun?

The spear in a standard gun is only supported in the mechanism and in the muzzle. To see this visually, try setting a long spear up on a table, lying it flat, and supporting it at both mechanism end and barb end with a matchbox. Now look along the spear, basically sighting along it from the mechanism end. You will see a prominent sag in the middle. The amount of sag you see will depend on the length, diameter and the stiffness/ tensile strength of the spear. If you move the matchbox at the barb end back towards the other box, the spear sag in the middle will decrease. At a point where the length of spear ahead of the moving box in roughly 1/3 of the total, the sag in the middle will be approximately equal to the now sagging end piece. This is again only really a factor with long spears.

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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.

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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.

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My railgun feels heavier than my standard gun but in the water it is much lighter and more maneuverable. Why?

When in the water the railgun seems lighter and more maneuverable than a standard gun because the barrel to spear ratio is greater and the internal diameter of the barrel is also larger, therefore giving it more buoyancy. The front of a standard gun is always heavier because the spear protrudes further beyond the muzzle. Some try to compensate by adding a foam piece to create lift. This does work but increases the end profile of the gun making it more difficult to maneuver.

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Why does my standard gun lose accuracy when I fit stronger rubbers?

Some standard barrels tend to bend when under big loads from strong rubbers, especially so with long guns. When you pull the trigger of a gun that has this problem, you release the compression on the barrel, which then straightens out. Because you are holding the handle at the back, the muzzle then moves the most, downwards, which in turn chops down on the spear as it is leaving the gun. This creates a bad wobble that slows the spear down and makes it very inaccurate.

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Is the railgun not noisier than a standard gun because of the spear being against the barrel?

Noise is definitely a factor underwater. A railgun is no different to any other, and it does make a noise. Fish are affected by noise but more so by the "pressure wave" that the rubbers put out when the gun is fired. The pressure wave moves through the water at the same speed as the sound of the gun and with greater force. No matter how quiet you make the gun you still cannot eliminate the shock wave the rubbers will create when fired. Some divers put a neoprene sleeve around their standard barrel to try to silence it. The problem with this is that the spear rests on it, therefore affecting the performance of the gun. The performance and "wet weight" of the gun will also vary at different depths because the neoprene sleeve will compress the same way your suit does.

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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.

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If my spear gets a little bent will it be able to still work in the railgun?

If it is badly bent then there is nothing you can do but try to straighten it. A spear with a very slight bend or twist, or even one that has been straightened and now has a few kinks, will still work in the railgun. The reasons for this is that the rail in relation to the rubber is set up to give a slight downward pressure, keeping the spear tracked. The center of the rubber when loaded is about 2mm below the spear center giving it the slight downward force.

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Why do most railguns only use one rubber?

Using one rubber on a gun helps with loading speed and reduces the drag when trying to swing the gun on a fish. This is only really a factor when using a long gun such as one with a 1.2m barrel. A long gun, with multiple rubbers, creates drag that will hinder your ability to swing. Through demand we have introduced a new muzzle which can accommodate an extra rubber.

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Why is it better to attach the spear line to the back of the spear and not onto a slide?

The line at the back is to improve the streamlining; a slide is generally bulky and causes drag on the spear when it is travelling through the water. Also when stringing the spear with the line at the back your range is one spear length better. With a slide, to get better range you need to have more than one line loop to the line release which takes up more time when reloading and can become a hassle.

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Is the wishbone notch in the spear not a weak point, considering the fact that the line attachment point is behind the notch?

The disadvantage of having the spear line connected to the back of the spear is the wishbone notch. This can get broken when a fish struggles in a cave and manages to wedge the spear and fight against it. There are many advantages to having the line attached at the rear though such as retrieving the spear when a fish takes it deep into a cave, since in pulling from the rear you have much greater control. A spear with the line attachment ahead of the notch will jam up much easier, and both fish and spear will be lost. Another advantage of the rear attachment is when shore diving in a strong current and you shoot but miss; a standard spear will hook up in the reef at the back and in very strong currents all your equipment can be lost. This has happened on many occasions on the Natal South Coast. Having the line attached at the back means that you could lift it off the reef more easily and just shake the barb lose if it hooked up on the bottom. Still another advantage to having the line at the rear is when the spear goes right through a fish that is shot at close range. When this happens you can retrieve the spear back into the fish. Standard spears will "T off" on the other side of the fish. Also, if a shark bites the fish while the line is through it, you lose your fish and your spear. If you are able to retrieve the spear back into the fish, the fish then fights on the spear and if a shark bites it you are more likely to retrieve your spear with maybe only a bend. We have recently developed a new wishbone notch system where the spear has a 2.5mm hole drilled where the notch would be, and a mushroom shaped pin is peened into place. This is then shaped to take the wishbone. The system means that much less steel is removed and therefore the spear is thicker at this point and much less likely to break.

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Why do most divers use monofilament nylon, surely it can cut on the reef easier?

Monofilament nylon is better in many areas; it has a much greater breaking strain than the standard polyester of the same diameter. It is easier to handle in the water because it is stiffer than other lines. When firing the gun, the spear with mono nylon will be much faster through the water than that with a polyester multi-fibre line. This is because being a mono fibre, it doesn't hold water like a multi-filament which would slow the spear down when the gun is fired. With polyester, the knot in the line is also larger than that of a crimp on nylon, therefore the drag is greater. In terms of being cut on reef, the best is to do a test at home with mono line and similar diameter polyester on a very rough rock or sharp surface. We have found mono line to be much better.

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Why do railguns not have screw-on rubbers in the muzzles?

The idea of a single looped rubber makes it more economical to produce and therefore less expensive to the diver. In actual use the extra rubber that goes around the muzzle gives extra drive. In other words, the rubber can be made a little shorter than that of a screw on set up, therefore giving you a longer drive that will give more speed to the spear. These muzzles are also designed to enable the diver to exchange rubbers easily in the water without tools if he is carrying a spare rubber clipped to his float. The length of extra rubber in the head of the muzzle is 10 cm.

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Why are single fixed barbs most common on railguns?

We have found that the vast majority of spearfishermen have at one time or another used or tried a drop head (slip tip). They virtually all change back to a single barb for a variety of reasons, the main reason being accuracy. Here we have found that it is very difficult to get the drop head to sit on the tip of the spear without any play (basically sideways movement). If you can get it to fit without play, then invariably it is too tight to come off resulting in the head pulling back through the fish and the fish being lost. The very tip has to be perfectly stable and central to maintain the straight flight of the spear. Even a very small amount of play will cause the spear to be inaccurate. This is because the extreme tip is what keeps the spear travelling true. A slight movement to one side or the other will cause a varying degree of inaccuracy depending on the amount of play. To show this you just need to sharpen a spear, which has a fixed barb, slightly off center, and you will see how much the accuracy is affected. Another problem with a drop head is the hassle. Slightly too loose and it falls off when you dive down, to tight and it stays on and pulls back out of the fish. This can be most frustrating. In terms of drag the drop head is bad, since the diameter is greater than the spear. A good head shot with a slip tip can become a major problem when it jams in the head. The only way to get it out is to cut it out. This can be difficult in the water and most frustrating when your buddy is still shooting fish around you. In terms of comparing fish lost with fixed barbs to those lost with a drop head, the majority of South African divers feel the fixed barb to be the better. In South Africa several large marlin, over 200 kg, have been landed with fixed barbed spears. Large marlin that have been lost are mostly due to the float system failing, not the spear. One of 500kg + was lost because the diver couldn't handle the fish in the water and eventually the boat crew "helped" by pulling on the float which parted company with the rest of the gear at an old boingie. Another disadvantage is costs; a fixed barb spear is much less a spear with a drop head.

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Can a railgun be loaded with the line under the spear?

No. Because of the rail, anything under the spear will cause it to lift up and shoot inaccurately. When loading the gun you must make sure that the line is on top of the spear and not under it anywhere along the barrel.

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While the line on top not interfere with the rubber during loading?

No, it will not interfere because it moves off to one side when the rubber is loaded.

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I have been using a standard gun for many years and now I find it difficult to aim with a railgun, is it just me or what?

Many divers have problems at first because the railgun is so different. When you are accustomed to aiming and using equipment that performs a certain way then change will feel strange and may take a while to get used to. Before getting further in this subject, let us try to visualize two geometric concepts, most important for a better understanding. 1) Horizontal plane: lean down at the head of a long table until your eyes level with the tabletop. Now everything you see on the tabletop, or along it, is in the same horizontal plane of your eyes. 2) Vertical plane: lean one ear against a long wall. Everything you see along or up and down the wall surface, like a picture, is in the same vertical plane of your eyes. That understood, be aware that the main problem area seems to be in the way some divers aim. Most look over the top of their guns while aiming, bringing the gun up onto the target. This tends to make it accurate in the horizontal plane because of the way you are looking over the gun, but not so in the vertical plane. We have found the best way to aim a railgun or any gun for that matter, is to not aim over the top, but rather along the side of the gun. What this does is it helps you to keep it very accurate in the vertical plane, which is much more important than the horizontal because most fish are much longer than they are wide. This is especially true with open water game fish that are difficult to get close to. When looking along the side of the gun, the rubbers, barrel and spear are all in the same [horizontal] plane as your eyes. All you have to do now is lift or lower the whole gun until it is on the same plane with the fish's spine. When this is in line, then the gun is moved from side to side to control the horizontal plane while keeping it in line with the spine vertically. In this way the shot will be on target with the spine but maybe a little out regarding the lateral placement. This lateral, hence horizontal, inaccuracy is not as important considering the spine is as long as the fish is.

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Is a small shock absorber on the shooting line necessary?

Some divers use them, but we feel that the mono line has sufficient stretch in it so you do not need one. The more you put onto a gun the more drag there will be when maneuvering and the more "fittings" that can fail. The only time one is necessary is when using Dynema cord. This is a very strong line, available in less than a 2mm diameter with a break strength of 260 kg. This cord has no stretch and therefore needs a line shock absorber (bungee) just to be able to stretch it onto the line release.

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What is the advantage of the clip on the muzzle where the spear line is attached?

This snap clip allows the diver to unclip the spear when he is having trouble getting the spear out and push it right through the fish, line and all, before clipping it back on. Another advantage is to be able to clip a spare spear on quickly when the old spear gets damaged or lost.

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How do I use two guns at the same time?

Many divers use two guns, the one gun being set up as normal with a float line, while the other is on about a 2m lanyard which is attached to a ring which slides on the other guns float line. This is to save having to dive with two float lines. Normally the diver will shoot first with the gun on the lanyard then, holding the float line with one hand to stop the other gun jerking, fire the other. This set up is mostly used where fish swim in big shoals and come past very infrequently, at least you could get two fish. Two guns also give you the advantage if the first shot was bad and you need to put in a safety shot. To dive with two guns though can be a hassle and some divers don't enjoy this.

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Why are plated spears becoming more popular than that of stainless steel?

Stainless steel spears are very good in terms of looks but when it comes to cost and stiffness they can’t compare. A stainless steel shaft can not be made as stiff as that of standard spring steel and costs around twice the price. The main problem when using a stainless steel spear is when it gets bent. The spear will still look good and the diver will be reluctant to change it for a new one because of this and due to the cost of replacing. A common problem now is the diver tries to straighten the spear and use it in this condition. He maybe able to straighten it to some degree but it is very difficult to straighten it properly. This will now most probably cause the spear to shoot inaccurately and, the place where it was bent will now be weaker and most likely to bend at the same place on the next fish if he is lucky to hit a fish accurately. I always liken it to the rod and line fishermen; very few use stainless hooks because of the cost and strength differences and rather use a hook as a consumable.

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Why do some divers use bungees (shock absorbers) on their float lines?

A bungee on the float line is a device, which acts as a shock absorber, taking the load off the fish between the gun and the float. When a fish runs, the bungee stretches and starts pulling the float at acceleration pace. The bungee is a one meter rubber with a compressed strong cord inside. It will stretch out to four meters. Some divers use two of these, one at the float end and one at the gun. These two would stretch out to eight meters, therefore extending your float line by that much.

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