I have been seeing and testing different roller spearguns for years. They are powerful and performing but they all have the same problem: a low trajectory. In some cases it is not that important but in others it makes the easiest catches impossible. It is probably for this reason that such a kind of speargun has not had the success it should have.


Lately I decided to study the matter in order to figure out what generates the problem and how it could be possibly solved and in the end I succeeded. I found the cause of the low trajectory and with a few changes I solved the problem. Here is my solution ...




One day, I was at sea with a friend of mine and I decided to pass him my rollergun in order to be able to film, close to the muzzle,  the shooting moment and this allowed me to realize what the problem was.


Analyzing every single photogram of the movie I realized that the muzzle gets suddenly pushed up when the bands end their run and the dyneema wishbone touches the metal stopper, a phenomenon invisible to the naked eye. When this happens the back of the shaft is still on the rollergun barrel, between the two pulleys to be precise, so the shaft gests an upwards slap that affects its trajectory. This also explains why a lightweight shaft is more affected by this than an heavier one.




How can this be sorted out? I had a plastic roller muzzle so I took a Dremel tool and some files and I dug the muzzle in the space between the two pulleys and shortened the muzzle output channel almost down to the pulleys axe in order to ensure that the muzzle can’t touch the shaft even if we tilt the gun.


The outcome? Just amazing! All the shots come out perfectly straight even with light shafts. To confirm this theory I made the same changes on another commercial rollergun I knew it was particularly affected by such a problem, however I had to cut a large part of the muzzle to get the same results and in the end I was finally able to make straight shots.



I called it "RollerUp", and it can be used with any rollergun. The wooden ones are even easier to properly shape, however, we need to find an alternative solution for the metal stopper. Unfortunately, some plastic muzzles need a definitive cut of the front portion to be fully and properly operating.


Here is a little drawing with the modification theory, the concept is simple: just consider when the shaft is about to leave the barrel and the last 10 cm of it are still touching the wood. Well you have to shape the muzzle in order to avoid it to touché the shaft even if we lift the rollergun about 1cm. The only way to do this then is to cut the spear-rail a few centimeters before the pulleys axe and dig the remaining portion of the muzzle the shaft slides on.



If you have any comment please post it down here.


Ivan Palumbo




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