quick question bout spear length and gun width

[joker]

hey all, i remember reading something somewhere about the relation between spear length and gun length but can't remember where- if i have a 75 cm gun, how long a spear would i need? And how wide should you build the total gun if you have a 7mm spear? Should there be about 7mm of wood on each side of the spear? thanks

[mishu1984]

it depends on whether you are trying to build an euro type gun or an american.
on average, on most euro type guns, the shaft protrudes from the barrel 30-40cm.
meaning, if your barrel is 100cm, you overall shaft lenght is 130-140cm

[spaghetti]

The correct spear lenght for a 75cm euro gun is 115cm.

For wood on the sides, there is no rule. It depends for example on how thick the wood, or on the sort of balance you want for your speargun (more stable, more manouevarable...).

In any case I wouldn't use a 7mm spear on a 75. Heavy spear+short band stretch=no velocity. I'd stick with a 6,5mm spear, but this is me.