Speargun upgrade

[Slinky]

Hi!

Bought a Seac Twin Thunder (50 cm) not to long ago and I'm now thinking to add an extra sling or replace it for a thicker one for a little more "bite".

My question is: Would a thicker sling do any negative effects on the gun?
I was thinking it might bend the shaft and loose some accuracy because of the speed increase since it´s only 6,25 mm?

I feel kinda stuck, and therefore I´m turning to the pro's!

Regards
Slinky

 

[e.m.p!]

Hi Slinky,

Adding rubber doesn't necessarily make your gun better (more rubber = more punch, longer barrel = more range). You'll most likely gain more 'bite' but sacrifice accuracy (as you figured already). It's not going to bend the shaft to start with since the rubber are loaded close to the trigger and there's no force applied to it. However, the increased power puts more stress on the barrel and bend it. Once released the barrel springs back to its original shape and will set off your spear.
Still your options are to replace the rubber with a slightly thicker one. I've replaced an old 16mm with an 18mm on a 90 and it didn't affect the accuracy at all – since the gun was almost underpowered with the worn out rubbers.
Your gun is only 50cm so it is unlikely the barrel will suffer with thicker rubbers. My opinion:
Go for it, put a bigger rubber on (no double though) and see what happens.

If you need more range you'll need to go for a longer gun though.

 

[Slinky]

Okay.
Got a 17.5 mm rubber on it now (original). Do you think a 19.5 mm is to thick? Seem to be my only option from the site I´m ordering.


Is there any balistic data to find where i can see how much i can load an 85 cm/6.25 mm spear without making it wobling when fired?

Another problem I have would be that the store can only provide me with either a 75 cm spear or a 90 cm of a different brand. So if i would need a reserv I´ve no clue if I should go shorter or longer.

Thank you for your answers!




Regards
Slinky

 

[e.m.p!]

Since your barrel is only 50cm long but likely (well is it?) the same diameter as any other models I don't think it would affect it too much, so no 19.5 isn't too thick but will be quite hard to load especially if short. Can't help you with some table or balistic data (google?) Anyway, it all comes down what your target species is - if you're hunting in caves I wouldn't replace the rubber for a stronger one as it just wrecks your spear.
Go for the longer spear as replacement – a longer spear is more stable 'in flight'. However if you prefer to "pick up" your fish off the seafloor and/or caves got for the shorter.

Just to clear this up again:
a thicker rubber will give you more punching power but sacrifices accuracy and won't give you range. Most of the shelf spearguns come with the best set up already, so it's a bit hit and miss to find out if it works for you. If it doesn't, extend your wishbone a bit (I never tried that though)