New gun build - 80cm

[portinfer]

Well I thought I'd revisit the 80cm wooden gun realm.

Originally I built this with Dave's help & advice (a legend):
https://forums.deeperblue.com/threads/teak-80-part-one-the-stock.63452/

And now a couple of people are interested in making a shortish 80cm type gun. I was going to make one alongside them and help as and when I could.

I was wondering if anyone (Martyn?) could weigh in on wood choice?
I was thinking utile / sapele / some kind of african brown wood.
I'm not sure on the difference between utile and sapele - or what we can get locally.

My original gun was teak. I don't think that it needs to be teak this time round & NP will charge a bit for teak.

Loosely based on a 115cm shaft and a 6.25mm diameter - probably the shark finned/tabbed ones from Salvimar.

Looking at the Ermes sub triggers but open to ideas.

Probably a 16mm or 17.5mm single rubber and single wrap / no reel.

Rough thoughts welcome!

 

[foxfish]

Any of those mahogany variants would be good or virtually any hard, hardwood.
For an 80cm I would definitely look at a reverse mech by far and away the best ones I have used are from here https://neptonics.com/product/tuna-trigger-mech/

 

[doyenofcastle]

I think abellan gun using utile /sipo for their stock ,for me i like gun to be more buoyant so i use iroko ,usually it need 0.6 ratio of lead to sink so small gun balance can be control

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[portinfer]

I've been thinking about this some more and looking at the spear tests on youtube by the user 'majdq8' and following his comments on spearboard (I have joined but it seems they take 3 weeks to authenticate new uers...).

It seems that a good approach to designing a new gun is to work out the spear / band / trigger first.

The videos by 'majdq8' are informative but focus on larger guns. You can kind of extrapolate details that might be suitable for a smaller gun but hopefully he'll test some smaller configurations at some point.

My 'Teak 80' is configured as follows:
115cm / 6.25mm Salvimar tabbed spear with 800mm of band stretch and a total length of 1070mm (cuttlefish shape - not high-mass).

From looking at the Abellan Robalo 90:
125cm / 7.5mm Hunt tabbed spear with 1000mm of band stretch and a total length of 1170mm

So it's 100mm longer than my Teak 80 but has 200mm more band stretch (and more mass to handle that).

So what is a good configuration for an '80'?
Could you get away with a 115cm / 7mm shaft with a reverse trigger to give 900mm of bandstretch?
Would that configuration with a 14mm small ID band be enough to power the heavier shaft (and reach terminal velocity?) or would you be overpowering the gun and either have to make it high-mass or accept big recoil?

These are the Salvimar 115cm shafts:
6.25mm / 115cm : https://www.subprof.com/en/spears/salvimar-laser-blade-shaft-mono-fin-53164794

6.5mm / 115cm : https://www.subprof.com/en/spears/salvimar-squalo-spear-with-shark-fins-11671

7mm / 115cm : https://www.subprof.com/en/spears/spear-salvimar-laser-blade-mediterranean-7mm-53168369

The Abellan guns have alot less spear overhang so it would be possible to increase the bandstretch from my Teak80 (235mm overhang).
Or would that not be a good config?
I.e. if you had 900mm band stretch would you need to go up to a 120cm shaft?

One of the guys planning to make a speargun like this wants to make a 70cm or 75cm gun. I think it's pretty hard to find a shorter shaft than 115cm (at least on subprof) and I'm not sure how to config that...

Hopefully someone will understand my ramblings!

 

[doyenofcastle]

I m planning for 78 cm gun also ,i choose iroko as its high buoyancy wood so even small dimension still ur gun almost float , all your design question hard to answer ,but for short gun what fish u hunt? Thin spear good for smaller fish heavier for bigger ,overhang for small gun with thin spear i believe should be 30 cm ,shorter for heavier (20 cm for 8mm)
2*14 300% for 7 mm 115cm is good? I cant say till i try mine ,if u need abellan muzzle i have extra but u need to shape it ,i attach my design for small gun and ermesub short trigger is good for small setup
i just want to ask how u gain more power from long stretch distance?rubber usually 350%strech for 120 cm and 70 cm gun so its expand 3.5 times giving same power !

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[portinfer]

@doyenofcastle :
The fish we hunt are smaller than 10 pounds / 4.5 kilos. Normally bass but some bream and pollock etc.

I'm thinking of the metal muzzle like on the Abellan guns but I'm not sure if the other two guys also making similar guns will go for a wooden or metal muzzle. I'll make one from stainless steel.

Which exact Ermes trigger are you using? I emailed Mario at Ermes and he suggested the new double roller trigger. I think it's a nice trigger but think that it is more suited for a larger more powered gun. Might try it anyway.

With the band stretch I thought that if you have a longer band then it would give more power.
So like with the Robalo 90 it has 1000mm of stretch at 300% and my Teak 80 has 800mm of stretch at 300% is that the same power? I think that the Robalo has more power - am I wrong?

I think that your 30cm of overhang is quite traditional. Certainly the Abellan guns have much less overhang.

I'm just trying to find out what is best with a 115cm long shaft - i.e. what is the best diameter to match with band dimensions (stretch and band thickness).

 

[foxfish]

I wouldn't worry about any of those things Ed, most configurations work more than adequately.
I don't like a long overhang, I use around 100 - 160mm but that is just my personal preference.
The last few guns I have built use a shallow 7mm track, firing a 6.5mm spear with a single 14mm band.
I really don't like using lightweight, overpowered guns, with long heavy spears as they are horrible to shoot & unnecessary for our short range hunting.
A nice 90cm (or 80) with a enough bulk to reduce recoil but long enough to send a short thin spear at a stable high speed.

 

[doyenofcastle]

double roller trigger for bigger guns ,any other trigger will work like ocean ,what about teak sea beam muzzle ?I have some and tried it in my gun and it work great .

 

[portinfer]

Well I finished building the gun back in spring 2018 nd hve been using it pretty much exclusively this year.

 

[portinfer]

I like the gun alot and have tried a few new things (to me).

 

[portinfer]

Here are some details:
Maple and Iroko for the body and maple and cherry for the handle.

120cm / 6.5cm Hunt Carbontech shaft. Single flopper (ordered one with the flopper underneath but it came with the flopper on top).

95cm of band stretch.

Ermes sub double roller trigger (what a great trigger!).

With a double wrap:
trigger -> flopper = 7m 20cm
gun nose -> flopper = 6m 20cm

Get a good solid pull at the end of a full range shot. Did some target shooting and good clusters in a 5cm ring at 5m from the gun nose.
Good solid flat shot.

Rubber is Cressi Pure Brown small ID 14mm. Impressed with this, easy to load and smoothly delivers the shaft accurately.
Currently at 310% stretch but can go up to 340% (or 360% with a 7mm spear).

The reel is a Hunt Carbontech one - I like using small reels because occasionally you need one (currents/depth/big fish/bad shot/weed etc).

 

[foxfish]

Looks fantastic Ed, I used one of those trigger units, (i think it is on Jersey mikes gun) but it was differcult to engage the spear without depressing the trigger at the same time, it might of settled in by now?

 

[portinfer]

This trigger :

No issues so far