Caleb's Rifle IRL Replica

DrunkenWrench

Hi there, I'm trying to make a real life version of Caleb's Speargun "The Redeemer". I've checked the model ig from multiple perspectives and how the whole reel and shoot mechanism works (Quite easy actually, but might have to undergo some more changes because 2 big gears won't do anything). I've made the sketch for the rifle, harpoon and the double barrel chamber modifications. One thing I do need to know, and that is the model of his rifle, I know, it's a fictive gun, but it must have some roots, and I hope someone would hint me a similar gun as his.