Light Blue Water gun dimensions?

[BLT]

Need a little help with some specs as per the title. All 6 guns I've made have been rear handle euro style guns.

I am going to build a light blue water mid handle gun, in the 59-60 inch range, probably running 4x 9/16th rubbers, 5/16th shaft. I want to taper the sides. Leaning towards a deep open track as this will allow a slightly thinner gun. I want the gun to track reasonably well. I've searched thru most of the builds on here, length is usually mentioned but nothing else.

What dimensions should I be aiming for with this gun? Height x Width at nose and tail?

Thanks

[Ric.Fallu]

I am working through the same process - trying to refine the design for a light tuna gun. What I want is something with punch at range, and long distance accuracy.

The first issue would be what spear to use. I settled on a Riffe 65 inch, 5/16 inch diameter (mainly because I have some). For the purpose of the design exercise, I used the one with the mono head, but I have other ones that take a slip tip.

The first thing is a stock that is strong enough to withstand the compression of the rubbers, and has enough buoyancy to float the spear. This means something at least in the range of 40 millimetres by 40 millimetres. I keep it this narrow at the muzzle to minimise water resistance.

Powering up a gun with multiple rubbers brings some problems with it. These come from recoil. One way of addressing recoil is to add mass to the gun. In a previous thread, Phil Herranen suggested that the gun should mass 3 - 4 pounds per rubber (thats 12 to 16 pounds for a four rubber gun).

How to sneak on the extra mass? How to do it in a way that doesn't compromise manoevrability? I decided to make the stock thicker at the butt (60 millimetres) and add extra side plates. I moved the handle forward about 30 millimetres. I kept the thicker areas near the handle to limit the effects on manoevrability of the extra water resistance.

Another problem comes from the thicker stock. The further below the axis of the spear the handle is, the more the impact of "muzzle flip" - which is what happens when recoil pushes the gun back, but its stopped by the handle. Muzzle flip lifts the muzzle, lifting the back of the spear making it shoot low. The higher the handle, and the more massive the gun, the less muzzle flip.

Perhaps another way of addressing the problem is the amount of spear overhang at the front. Guns with short overhang tend to shoot high. Its not the gun as much as how they are sighted along, but the effect is still the same. Possibly, you could compensate for muzzle flip by having short overhang.

The other possible problem with powering up a spear is "spear whip". Its as if the spear is a bell - when it is slammed on the back by the rubbers, it rings, and vibrates. If the tip vibrates from side to side whilst the spear is in flight, it wont be accurate. Spear whip can be a real problem in thinner spear, even with one rubber, but I really haven't had enough experience with bigger guns to predict how a 5/16 inch spear will whip with four rubbers.

Anyway, I am building several guns (one of which was posted earlier with the title of "light tuna gun" it shouldn't be too hard to find). The guns are basically similar, but have differing mass and different spear overhangs. I am also experimenting with the benefits (or not) of adding a "wave collapser" along the spear channel. I will target shoot with the guns and compare.

It takes a while to finish these guns. I have done one, and am more than half way through the second. But when I finish all three, I plan to post the results of the experiment. In the meantime, I also plan to post pics and descriptions of each gun as I finish them.

Ric

[BLT]

Thanks Ric
I've read your posts on here and on SpearOz.

I've just glued up my stock which, once put thru the thicknesser, will come out at 56mm wide x 45mm high.

I used 15 laminates in the stock. I've also sandwiched in 2 layers of carbon fibre into the length of the stock; more for re-enforcement of the muzzle. This should allow me to taper the gun more, and keep the integrity of the muzzle.

[Ric.Fallu]

Have been working on the next iteration of a light tuna gun (as mentioned above). I balanced it the other day and went to add lead. To make the pockets to take the lead, I chopped out timber from the stock. Being an old fashioned sort of guy, I used a chisel to remove the wood. Because I needed to add a lot of lead, I cut deep, right through a layer of fibreglass tape I was using as stringer between laminates. It really destroyed the edge on my chisel. This was not a disaster as I went back and ground the chisel down a bit and put a new edge on it, but it occurs to me that making a new edge is not as easy or cheap if you want to chop through glass (or carbon fibre) with a router tip.

Just something to keep in mind when weighing up whether or not to include stringers between laminates.


Ric