Welcome to my "ible" #36.
The finger line release I've designed doesn't modify in any way the safety of my speargun. In some countries (Italy for example), you have to be 16 years old to use a speargun, that is still remains a potentially dangerous weapon and has to be treated with respect. "Never walk about with a loaded speargun or leave a loaded gun lying about. Always unload before leaving the water. Never point a speargun at anyone, and take care when firing in murky water, you may easily hit one of your companions and cause injury."
I've found my Seac Sub Killer 60 Sling Speargun in the attic (last time I went fishing with it, was 25 years ago),and I decided to restore it.
I've bought 2 brand new rubber bands, but I realized that the finger line release was missing (the Killer 60 wasn't equipped with it).
I've found a brilliant solution to this problem in an underwater fishing forum, suggested by Claudio.
By the way, many thanks for that!
Step 1: Print It... in 3D!
I've really liked this idea, but I didn't want to build it, as I thought that designing a 3D printing version of it, would have been much easier. After a bit of drawing, I've designed the finger line release and now the part is available here...
ready to be downloaded.
I've printed in ABS (in Nylon would have been better) and it's very robust, but I've printed twice to have a spare part...
you know, just in case.
Print in 3D your finger line release, here...
Step 2: Install It on Your Seac Sub Speargun
Drill a hole close to the trigger, double checking the distance and the alignement.
You basically want to release the base of the finger, as soon as you press thre trigger.
Add a M4 Nylon nut, a bolt and 2 washers, to attach the finger line release to the frame of the speargun.