I used small Swimaster (JBL) guns and never had a problem with the triggers. They seem to tolerate loads well. If there is a problem of resistance under load the trigger parts should be removed, cleaned, and working surfaces polished or honed. One caution, remove any stainless screw that penetrates the aluminum grip and coat the screw with SILICONE grease. Silicone only.
Do not use mono. It is stiff and slippery and has low tensile strength. One abrasion will break it. Use KEVLAR 500 pound line and you will thank me. If you mount a reel (unlikely on small gun) do NOT use kevlar on the reel spool, use nylon. Kevlar will jam up the reel. Anyway, continue to use kevlar as the shooting line and connect to reel line with a swivel.
I agree, use 5/16 spring steel shaft. If gun has 3/8 replace with the thinner shaft.
Use JBL rockpoint detachable head (they call it 'breakaway' for some reason). Also get a 'free shaft' with single LONG wing but attach the freeshaft to the gun with a string. Before you do that slide on two rings from the rear of the shaft. The second ring, just below the wing, must be soldered to the shaft. Glue a small piece of foam rubber under(inside) the wing. You now have a single wing which can be clamped down by the sliding ring. The sliding ring is prevented from moving back down the shaft by the soldered ring. This sliding ring moves over the wing and allows quick removal from the fish. Moreover, and very important, the wing will spring out and toggle the fish. Even more important the ring will prevent the wing from acting like a foil and deflecting the shaft in flight. If you wish to string the shaft get one with a hole drilled through. Biller does this. This modified free shaft is unbelievably fast and effective and will hold a fish better than any other type of fixed head/shaft. Use two heavy rubbers, if you use three the spear will string the fish (go through) and create a mess. If you want to use without string this is best done in clear water. I recommend the Biller freeshaft (without threaded tip, plain tip with single wing). I believe it will fit the JBL sear box. I don't have time to explain the physics of the above conversion. I should say that a plain shaft without conversion will work in most cases but so will a plain threaded shaft (no tip) when used as a freeshaft on small snappers and groupers. Having learned from previous posts of this nature I offer this: if you don't want to do the mods don't do them. If you decide to do it and need clarification PM me anytime.
Don't worry about the noise generated by a metal gun. The wood gun manufacturers are blowing smoke up your butt. The only things which spook fish are bubble blasts, hand movements, swiveling the head, barrel swing, and especially the sight of an arrow flying though the blue will cause the school to flash. Fish are actually attracted to certain noises, most of which we can't hear. I might add that some divers paint their guns black. Apparently the movement of a bright metal gun spooks fish quicker. Also, do not use amber rubber, if possible, it glows undewater. Instead, use Biller black coated amber rubber.
Pesky
salty:
Watch out for that third band on a the JBL. Unless you have a XHD trigger mech. you may have overpowered the gun, this will cause the trigger mech to "lock up". I used a overpowered JBL once and missed out on a 7 pound fluke once because the gun would not fire.
I have a JBL 38 special Northwest XHD. I have a few modifications that I would like to sugest.
First replace the braded line with mono, its easier to work with and will allow the spear to move faster.
Get a thinner spear, this will also allow the shaft to move faster and go farther with the standard bands. Also with less bands reloading is quicker when the fish are all around.
Consider a spear with out a removable tip, get a single flopper style spear there quick and easier to manage when removing from a fish.
