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 Post subject: Tuna gun build
PostPosted: 02 May 2012, 14:59 
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Joined: 23 Nov 2007, 12:20
Posts: 305
Location: Melbourne/Sth Gippsland
I wanted a gun to take southern blue fin tuna.

A gun should be tuned to match the fish and their environment. Where I hope to go, the tuna can be large, but it will be unlikely to encounter a real monster, so I built the gun with a 20 to 30 kg tuna in mind. The tuna are found near the edge of the continental shelf, so it’s a true blue water environment. I am unsure whether they will be encountered head on/from the top, or from the side, so I don’t know if the stalk will be “extend and shoot” or “swing and track”, or both.

I wanted a powerful gun, but nothing too heavy. My thinking was a four rubber gun, pushing an 8mm (5/16 inch) diameter spear, fronted by a slip tip. The stock length (from front of mech to tip of muzzle) should be about 1.35 metre.

Before starting the build, I named this gun “Death Descending”.

Since it was an experiment/prototype, I didn’t want to use fancy timber or joinery. I made it from DAR, KD, radiata pine, purchased from Bunnings. I tapered the central strip, and laminated it between two others. I used fibreglass plasterer’s tape as stringers. West epoxy holds it together. The pine strips came in a width of 40 mm, but I wanted a bulkier gun, so I laminated-on some side strips. Cheap timber or no, I still think the pine looks OK.

I don’t care what other people say, real men make their own handles. It is mortised into the under plate, and secured by a dowel. It fits my hand, and fits it exactly. I angled it back a little more than usual to assist in dissipating the recoil.

Seems to me there is a 1950s “spacey”, “ray gun” aesthetic to this gun’s appearance, and I like that. Not that that will impact on how well it shoots.

I used a Riffe mech, with a 5mm stainless steel push rod.

There are four 16 mm (5/8 inch) rubbers at 3.5 to 1 stretch. The bridles are “starter motor” braid.

The spear runs in a channel, about 8 mm deep. This was cut with a hand held router. In three places along the channel are “spear whip inhibitors” mini enclosed tracks, about 20 millimetres long. The spear hole through these is 9 mm. I fabricated them from acetal (delrin) plastic, fitting each individually to align the spear in the channel. This is an unconventional system, but it has worked for me in the past.

I plan two wraps of shooting line.

There is a hole above the handle to take a rubber break away, but I think that for my tuna fishing expedition, I will use a tethering rig.

I have not yet balanced and ballasted the gun. It has yet to get wet. I don’t know how much it will finally mass, and how it will shoot. Sticking my neck out and making predictions is a sure way to look silly, but it’s also the fastest way to learn how to build a better gun. My guess is that:
• Death Descending will shoot a little low, but once that is compensated for, it will be consistently accurate. I make the prediction based on the distance of the handle below the axis of the spear, and the length of the spear overhang at the front. I also suspect that if the spear overhang was a little shorter it should shoot flatter.
• there will be noticeable recoil, but nothing too obnoxious. I might have made the gun a little bulkier.

But, time will tell. I need to finalise the gun, and target shoot.

Once its done, all I will need is a boat trip out there. If anybody wants a paying passenger, I can be contacted on ric.fallu@bigpond.com


Ric


Attachments:
ready for ballast LH.JPG
ready for ballast LH.JPG [ 32.37 KiB | Viewed 3415 times ]

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Ric Fallu started spearfishing in Pt Phillip in the early 1960s, and never really stopped
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 Post subject: Re: Tuna gun build
PostPosted: 03 May 2012, 09:49 
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Joined: 03 Aug 2006, 09:55
Posts: 622
Location: Melbourne
Good to see you last night Ric and what a really solid piece Death Descending is
That rear part of the stock should take much of the recoil from the 4 bands
I really would love to be part of the first shooting tests to see your process of fine-tuning; give a call when you think you are ready and we could take the boat out where there is a bit of depth
Ps. Loved the graphics

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 Post subject: Re: Tuna gun build
PostPosted: 03 May 2012, 17:23 
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Joined: 16 Jun 2009, 14:24
Posts: 228
Hi Ric!,
nice work (as usual). Got any top-down shots of the "spear-whip inhibitors"? Be interesting to see how you've done that.

Also, very happy to see you are using the radiata pine from Bunnings; picked up a couple of lengths of it (1.2m x 19mm x 42(?)mm) a few weeks back, but wasn't sure if it'd be up to the job.

What I had in mind was something I could take interstate (e.g. had to knock back an offer of a trip to S.A. a while ago, partly due to my 1m Basik not being up to handling the larger species the other travellers were intending to target).

As a result, am tossing up between buying a handle (and therefore being able to use the full 1.2m length of the stock), versus just the trigger mech and then constructing a sweet custom wood handle like the ones you do (would end up with ~ a 1.1m if I did this?).

Something that could handle the local kingies, and possibly even a small tuna would be good.

Am thinking it would it need to be at least a 1.2 though to have a chance of taking these kinds of fish.

After having a read of your threads on "Shaka" and the "Home made rail gun" <- you never named that one?, it sounds like I'm roughly on the money here with the materials I have and the use I have in mind for it?


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 Post subject: Re: Tuna gun build
PostPosted: 05 May 2012, 11:03 
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Joined: 23 Nov 2007, 12:20
Posts: 305
Location: Melbourne/Sth Gippsland
I took the gun to the Southern Freedivers club meeting. (Its not always wise to show off an unfinished gun, but what the heck!) Anyway, there were several comments:
• The spear, trigger and line hook were stiff – this was due to swelling caused by epoxy and varnishing, and should be rectified by judicious sanding and filing later
• It was in !#@!*! pine. If this gun shoots well, I will prolly make another with flasher joinery and timbers. Pine doesn't have the Wow factor, but it works well enough
• The spear whip inhibitors may not withstand the rigours of firing the gun. Time will tell on this one, but similar arrangements have lasted OK in other guns.

As he commented, Pietro liked my hand drawn graphics on the side of the gun.

There has been a big dump of rain over the last few days, no doubt dropping the salinity in nearby seawater, so I will have to wait a few days before I try to ballast and balance the gun.

Will report further on spear whip inhibitors after I test fire the gun.

===========================================================

As far as a Vic kingy gun goes - depends a bit on who you talk to - a New Zealander would say an 80 cm gun with a 7 mm spear is quite adequate, or an American would recommend a 1.4 gun with four rubbers and an 8mm spear.

Recently was at the Prom (courtesy of Rob Torelli - thanks Rob) and had a chance to try some Americano style classic woodies - both with 8 mm spears, two rubbers, but one 1.3 long and the other 1.1 long. Both took kings adequately. In the medium viz, I didn't notice a lack of range for the 1.1, but I did notice the extra water resistance trying to swing the 1.3. I have been thinking that 1.2 would be a good compromise for use in Vic and southern NSW. (but if I was targeting pinkies, I would find that style of gun too heavy I think).

Others may have opinions on this.


Ric

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Ric Fallu started spearfishing in Pt Phillip in the early 1960s, and never really stopped


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 Post subject: Re: Tuna gun build
PostPosted: 06 May 2012, 13:05 
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Joined: 16 Jun 2009, 14:24
Posts: 228
:)

Cheers for the feedback Ric! Might drop you an email as I get closer to building to make sure I've planned the finer details correctly.

Sure there's flashy/exxy timbers out there, but I actually quite like the look of well-finished pine. And at about $2.20 for a set of barrel timbers, I'm not complaining.

It's a pity you couldn't try out your new rig on the kingies during your recent Prom trip. But on the other hand you wouldn't want the kingy-of-a-lifetime to swim into view whilst you were trying to figure out the balance and ballast of a small tuna cannon in your hands.

Thanks again for the feedback, hope you get to try your new toy out on it's intended targets soon & Cheers!


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 Post subject: Re: Tuna gun build
PostPosted: 05 Jun 2012, 11:19 
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Joined: 23 Nov 2007, 12:20
Posts: 305
Location: Melbourne/Sth Gippsland
Weather has been atrocious lately, and I need clear water to do a target shoot with this gun, so that has been put off. I have test fired it in dirty water though. There was some recoil, but not as much as I might have expected. I didn't actually try doing it, but I suspect the gun could successfully be fired single handed.

On the first fire, about a millimetre/millimetre and a half of the plastic on the left hand side of the front guide was sheared off by the shark fin tags on the spear. On subsequent firing, no more was removed. I think it may have found its own equilibrium.

With two wraps of shooting line, the tip of the spear reaches to about 8 metres from the end of the muzzle. After a shot, I could feel a slight tug on the gun from the spear running out of line, so it shoots that far, but prolly doesn't have much penetrating power at that distance. My test fire was in water with 2 metres viz, so I couldn't see what was happening.

I would feel confident shooting at a big fish with this gun. Although I don't know how straight and flat it shoots at distance. Until I can do a target shoot, I would wait until the fish got close.

I am moving onto gun tuna number 2 (named Ming the Merciless). This gun has much the same specifications, but has more added mass, and it will be interesting to compare any extra range and accuracy, as well as reduced recoil. Will post pics and description in due course.

Ric

Ric

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Ric Fallu started spearfishing in Pt Phillip in the early 1960s, and never really stopped


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 Post subject: Re: Tuna gun build
PostPosted: 05 Jun 2012, 16:08 
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Joined: 08 May 2010, 20:11
Posts: 252
lol i love how you name them "thumbs up"


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 Post subject: Re: Tuna gun build
PostPosted: 29 Jul 2012, 14:29 
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Joined: 12 Mar 2012, 22:41
Posts: 55
Death Descending and Ming The Merciless....

Hows about Meadowsweet Buttercups or The Little Ballerina? At least with those latter names I wouldn't have to feel like I should be wearing an eye patch and listening to Death Metal.


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 Post subject: Re: Tuna gun build
PostPosted: 29 Jul 2012, 17:54 
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Joined: 16 May 2012, 16:35
Posts: 40
I see you've incorporated a tea cup into the front handle. Maybe you could incorporate this feature into the name.


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