Why US speargun use square cut sear tooth and Europeans used angled teeth.

[popgun pete]

We can see the sear box tunnel goes back a long way with this 1940’s Hurricane speargun from France. This gun originally has a tubular frame shoulder stock, like a carbine or rifle.

[popgun pete]

Reverse trigger mechanisms that are frame lock can be improved by placing a floor in the sear box just forward of the spear tail latching position, this could even be a couple of transverse pins that go under the shaft as long as they cannot hook the shaft tail notch. Or as the rectangular sear box mouth is no longer necessary they could just close the gap on both sides and cup the shaft tail.

Looking at a forward trigger mechanism like the JBL M series trigger designed by Bill Kitto and Mori you can see that the shaft will be travelling on a guide track almost as soon as it leaves the sear box mouth. Also the pressed metal housing cups the spear tail except for the gap where the levers sit, so as the sear tooth descends the shaft tail will be wiped free of the tooth without any snagging.

By way of contrast if a reverse trigger mechanism with no sear box tunnel has the spear tail stick with the high contact pressure onto the tooth then it can go down with the tooth, the deflection will be very small, but can translate to big changes down range.


Now the above trigger mechanism looks like it has a floor, but it is the top of the sear lever which falls away with the mechanism's release. I am not saying the above mechanism is faulty, I just use it being emblematic of a long sear lever, reverse trigger mechanism. Nearly all the folded sheet metal trigger mechanisms housings are made this way.

Similarly the roof of the sear box should be extended forward, right now many of them are too short. These changes would then create that long missing tunnel that aids shaft separation from the sear tooth and stability of the shaft exit.

[popgun pete]

Just as a guide to nomenclature I use this sketch that I created for the Double Roller triggers.

[RichT]

great info! Thanks

[popgun pete]

To my knowledge the only star wheel sear lever that had survived into recent times are the Balco Sub “Thunder” and “Arrow” spearguns, the former has a cocking stock, and the latter does not. This gun’s trigger mechanism is actually a frame lock by courtesy of the little bump on the front of the trigger, just above where you pull on it with your finger.

[popgun pete]

Interesting to note that Sigal Sub have incorporated a floor in their Nemesis gun's sear box. You can see it here along with a spear latched in the gun.

[popgun pete]

A gun from US company Scubapro that departed from the square cut sear tooth norm is the Panther gun made from a skinned foam plastic reinforced with fiber glass and produced by injection molding. These guns use a variation on the two-piece trigger mechanism that dates back to the Undersee cam lock unit, but curiously have a rounded sear tooth. That means the spear tail is trying to jump the sear tooth, but it has no hope of doing so because the mechanism pivot pins hold the inverted U shaped sear box roof in the gun. In order to do that the pivot pins sit on the same horizontal line, normally the trigger pivot pin sits higher than the sear lever pivot.

This trigger mechanism does not obey the mechanism rules completely, but there is a reason why it works. Some of the load that would normally be transmitted to the levers is being taken by the sear box roof which means less through the levers. The trigger retention step is matched to the travel arc of the trigger, so a force component still directs to the trigger pivot pin and that is enough to keep it locked. That orange vector on the diagram shown with an X never gets big enough to shove the trigger back. Once the spear is on its way all the force is directed forwards from the bands, while at the muzzle anchor the bands try to push the gun backwards, as do all guns.

Why make the gun this way? Well it continued the lineage of a deep handle and a very long trigger as used in all the Wally Potts guns going right back to the very beginning. Still available today the Panther is a good gun and very well made. It would need to be as its injection molding dies cost a mint, enough to buy a European luxury car in its day. A very advanced gun using precision components, but only made in two sizes, a 26 inch and a 36 inch.

[popgun pete]

Originally Posted by popgun pete

Just as a guide to nomenclature I use this sketch that I created for the Double Roller triggers.

The roller tooth improved the mechanism gearing.

[popgun pete]

And to spell it out for those who may be wondering what I am talking about.

Note the system could use something else besides a roller, it just needs to be free floating and fit the spear tail notch and also an angled "tooth" in the sear lever arm which here is a semi-circular dip cutout. A roller is the simplest shape for eurogun spear tail notches which are that shape anyway.

[popgun pete]

For example.

[renepotvin]

Originally Posted by popgun pete

The next evolution was the two-piece cam lock trigger which had the advantage of using existing square cut tail spears, the most famous being the Undersee trigger mechanism invented by Denny Wells. Another was that used in the Lyle Davis gun, this being a formative period for all modern band spearguns. The sear lever now rotated separately in a sear box with a roof and floor so that the spear tail was wiped off the rolling sear lever tooth and the spear was allowed to fly from the gun.

Well, it was an old design used on crossbows in europe since before the romans... and the chinese had this 3 part design before, and it didn't require springs! This one is from 6th century.





In the USA, at the beginning of the last century, there was this guide to make you own crossbow with a 2 part mec... hardly an invention by then (In cm no less!)

[popgun pete]

The crossbow mechanism fires the bow string, which pushes the bolt or arrow and uses gravity to help set it by swinging the levers. The speargun had to fire a very heavy projectile and needed a long draw of its bow, thus that bowstring needed a long pull. For a man carried device that draw needed a long reach onto the stretchy bands that replaced the bow, hence first we have the hook, that is replaced by the throwing plate and ultimately the wire wishbone.

The Arbalete replaced the side-slotted barrel elastic gun which had first been taken underwater by Commandant Yves Le Prieur.
https://spearboard.com/showthread.php?t=198019




This big gun used a pull down sear lever which had been used in the spring gun, once it is realized that the trigger mechanism could hold the projectile everything changes. The twin teeth of the crossbow mechanism don't lend themselves to such an application as they are strictly bow string holders.

[popgun pete]

Trigger mechanisms are discussed here, including the Chinese crossbow mechanism.
https://spearboard.com/showthread.php?t=141058

[popgun pete]

A crossbow mechanism gun for fish shooting, but not an underwater weapon. Made a decade or so back.

Saw one where an optimist had cut the cocking stock off, but just looking at that gun I doubt that it ever made it into the water. Mechanism would rust being not designed for immersion.