Alison makes good sense when she suggests not making a trigger if you don't quite understand exactly how it works.
A great alternative...
There's a very slick and simple type of speargun called a Hawaiian Sling. They're capable of taking very large fish and work really well on the typical reef fish that most people shoot for the dinner table. You actually shoot this type of speargun much like a bow and arrow so you'd probably really like that style of speargun.
A Hawaiian Sling would make a great first speargun project. I may soon build one for myself just to keep in my vehicle for those spur of the moment spearfishing opportunities.
