Interesting post Dave. Lots of insights. I'd never heard of the reverse grip technique before; it sounded impractical but I just tried it with my speargun and I see what you mean. Excellent.
I wonder what guns you saw that did not overhang - pneumatics or short trident head cave guns with a thick spear perhaps?
OMD, I usually aim along the side of the spear gun - as I read the Len Jones book when I first started (the idea being that vertical accuracy is more important as fish are long & thin). I don't aim real carefully though, I just use it as a rough guide - with the long barrel & an extended arm it works reasonably well.
Yes, I think 40cm overhang is normal for a band-powered gun (perhaps slightly less for a shorter gun & slightly more for a longer gun, but usually 40cm). The idea is (at least partially) to offset a natural tendency for the spear to droop down in the middle, between the rear end support & muzzle. Interestingly though, railguns, which support the spear along the entire muzzle use the same overhang length. This might partially tradition and so that folk moving to and from rail-less spearguns don't notice much difference when it comes to aiming. I did ask Rob Allen whether using a shorter spear would cause any problems and he reckoned going 10cm shorter should not be a problem but he recommended not going any shorter. I don't know the reason why though - perhaps the reasons mentioned above? Or perhaps it gives you some of the benefits of a gun 40cm longer without many of the disadvantages? I thought it might be interesting to use a spear with little or no overhang - so the overall length of a 90cm railgun would be that of say a 60cm speargun. It might be more versatile - although the 90cm barrel would still drag.I have a 75cm gun with a spear that comes a 6-8 inches from the muzzle, which as far as i can tell is the norm.
I have seen guns with the spear that pretty much ends AT the muzzle with the barb held within the gun. Is this a good thing/bad thing?
I wonder what guns you saw that did not overhang - pneumatics or short trident head cave guns with a thick spear perhaps?
OMD, I usually aim along the side of the spear gun - as I read the Len Jones book when I first started (the idea being that vertical accuracy is more important as fish are long & thin). I don't aim real carefully though, I just use it as a rough guide - with the long barrel & an extended arm it works reasonably well.