How to correctly power a speargun

I have a cressi mohawk 140 and it shoots like a laser, in fact i would rate it as good as a RA, check to see if your spear is straight or not, i use a single 16mm band on mine and it is more than enough, 2 bands would def. overpower it. You could try using ihabs method for getting it the way you want it

Quote from Ihab

Diesel, there is a relationship between band, shaft & gun mass…to balance the outcome for accuracy…just play around with band stretch till you get the least recoil with the shortest bands.

This is how I would do it.
- Calculate band length according to the regular 3:1 stretch ratio and stick to 16mm bands….at this -stage, it doesn't matter what brand of rubber you're using.
- IMPORTANT….for wishbone, go for the Italian style wishbone where you have a knot at the end of each rubber and a separate cord attaching both ends of the bands (if you need help making this knot let me know).
- Tie the cords with the end knots so that the total length of each wishbone, from rubber end to rubber end is no more than 12cm (assuming you're using 2 Bands)
- Test your gun in very stable conditions…I use a plastic water bottle in a pool.
- If you miss after several trials or gun is shooting a bit low, replace the cords and this time increase cord length so that the distance between each rubber end is 14cm…i.e., go in increments of 2cm.
- Depending on your gun mass and shaft size, at one stage your gun will shoot smoothly.

The Italian knot makes it very easy to change the cords on location…actually, I would prepare several different cord lengths before testing.

Good Luck

Ihab
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Those Cressi handles are picky on what shafts you can use.

Quote from ollie

CWW yes i have noticed that and had to grind 2-3mm off the end of the RA shafts for them to work smoothly.

Jono is there any chance you can post a pic of the wishbone setup you are talking about, i think i understand but am not quite sure are you saying that you cut your rubbers and change the band stretch by cutting your bridles?

I am not a huge fan of the mowhawk as it is just a rebadged orca thula and my plastic coating on my barrel is not fully stuck to the aluminium.

Also the rail is not deep enough so that if the gun was not held spear side up for the whole dive the spear would fall out of the rail and sit in one of the other grooves in the muzzle, i fixed this cheaply and did a little surgery to the muzzle by cutting everything above the rail off and inserting a SS pin to guide the line to convert it to an open muzzle this holds the spear in place.

Apart from those things the gun has taken heaps of fish for me and is more than capable just won't be buying another one is all

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You put a loop insert in each end of the band and tie the constrictor knot, from that loop yoy play with the lengh of the dyneema bridle.;)

OK, single 16mm does not provide suficient power, and double band is too much, 2 X 14mm bands and a 7mm shaft is a nice proved by me set up, that you can try:).

Cheers.

Quote from ollie

oh im not sure if you read i have 20mm band and an 18mm band which can also be re cut, does anyone have length of rubber/s chart for pipe/euro guns?

Two 20mm or two 18mm or anything in between is too much for an euro pipe gun.

Here is the chart of BEUCHAT for 18mm bands
GUN LENGH
85 56cm
95 62cm
105 68cm
115 75cm
125 83cm

This is from rich's thread on SB ...

The wishbone is loose on both ends and you tie it with a (sort of) overhand knot. If you're using wire wishbones, I guess you're just stuck with tying them in and letting them rot on the gun, or you're going to end up cutting the slot and figuring a way to reinforce the muzzle with a bolt and a spacer

Cut and taper the bands, shove the looped knot into the band and tie as usual. Pull the loop tight:

Cut the dacron wishbone and melt the ends with a lighter. Run the end of the wishbone up through the spectra loop & back behind. Loop the wishbone underneath it's self and pull it tight.

The hitch never slips but it's easy to untie and you can choke down on the wishbone easily if you want to shorten it for a bit more band pull. Takes about 5 seconds to install or remove bands for storage, and the spectra and dacron will long outlast the life of the rubber.

This was an awesome post btw rich just had to re-share it.

Jono

wishbones are too long

Quote from greekdiver

wishbones are too long

Yeah, it was just a mock-up for the pictures I shot.

The loops are too long also...

Shorten both, and you'll be golden

Love the tutorial rich. Helped me learn a lot

rich--yep, that's the way I've been doing my bands for years. Works great. Thanks for the picture tutorial :toast2:

Jono---thanks for posting the band charts bro. I'm sure that will b helpful to many here :toast2:

Managed to dive on Wednesday before long weekend and shot a snapper and giant cuttlefish (in Adelaide), i was in Sydney over the weekend visiting family but didn't have any dive gear over there. Next time i will def. drive so i can dive as well.

Snapper was shot free swimming, i don't tend to burly to much over here due to the danger of GWS. It went 42cm on the brag matt, not huge for over here but def. legal. The cuttlefish made the snapper look small though.

There are others who can better answer your question but i always thought if your shooting high it is mainly due to muzzle flip when firing due to excess recoil, you can fix this by either adding mass to your gun (which is easy if it is timber but harder if it is a pipe gun). Shooting low would mean that you possibly need to either adjust your aiming or try powering up a bit by shortening the rubbers etc.

Everyone aims differently so its a bit difficult to give a specific answer.

Good Luck

Jono