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Don, I would love to know about the results that you guys came up with in your testing. I assume that you looked at shaft velocity with different diameters.

What about the impact of a larger diameter tip on the speed of a shaft? Does the mass of the shaft or the diameter of the tip (the amount of water which must be moved) have a bigger impact?

What factors did you find to be the most important in achieving guns with the best accuracy in terms of handle height, limit of power vs. gun weight, band slot height, etc?

Impact of enclosed track?

The list goes on and on. Bottom line anything that you can share would be greatly appreciated.

Chad

Hell Yeah!

I wonder if anyone has ever setup a high speed (super slow motion) camera underwater. It sure would be nice to be able to see what is happening during the firing of a speargun. When watching an arrow shot from a bow is super slow motion, I was stunned at how much the arrow was bent. I wouldn't be surprised to see that there are things going on that we didn't fully expect - especially with "high power" guns.

Jeff, if you want to come over sometime soon, we could take some video that will at least show whether or not the front of our guns are kicking up during the shot. One of us can film the side of the gun while the other shoots at the target. I have a new HD underwater video camera which might capture some decent data. You need to pull the trigger on the hybrid don't you?

Maybe this is a good place to make a distinction. I think that muzzle flip is a very real phenomenon. I'm just not sure that it's due to parallel (or non-parallel) band pull. I haven't used band elevators, but I have read where others swear by them. Maybe there is another interaction at work. Maybe the band elevators (or parallel bands in a euro) do something else to reduce muzzle flip.

For example, the motion of the bands at the end of the firing sequence. Or the way they disengage from the fins / notches, etc.

As Davie noted in his calcs, it's pretty small.

If we had a band slot 1" below the shaft, and the bands were stretched 40", then the angle would be about 1.4°. If we had a 200 lb band load, then the vertical component would be 200 x Sin(1.4°) = 5 lbs.

But here's the part that has always confused me. That small vertical force only serves to pull the shaft and stock together. Whatever force is pulling the stock up, is exactly the same as the force pulling the shaft down. They are already touching, so one cannot be pulled closer to the other. So I don't understand how the vertical component of the band force can generate muzzle jump, even if this component were large.

I can see it if this were an old style gun where the spear were unsupported over much of its length, because then there can be relative motion between the shaft and stock. But that's not the case for most guns.

In my head, it has always seemed that muzzle jump had more to do with the way the recoil force acted about 1) the grip, and 2) the gun's center of mass. Davie points out that the mass of the gun is small compared to the mass of the diver, so it would seem that the height of the grip would dominate. If you follow Davie's analysis a little further, it may even reach the theoretical conclusion that you could reduce muzzle jump by LOWERING the band slot, to put it inline with the grip?

It seems to me that if the Band Slot, grip, and Center of Mass of the gun were all in line, then you should have no muzzle jump. I have wondered if the way the bands jump around at the end of their contraction could somehow cause the muzzle to move. But I don't know how this would be different for inline versus normal bands.

Dan - Can you say if the original idea (one band in each hole) would have been equally effective if you had arranged the holes as you meant to?

Tough to say. These spots are heavily fished H&L. We rarely see other divers, but the location is obviously not a secret.

Unfortunately, this rather substantial pile of rubble seems to have disappeared over the summer.

Two dives, on the same wreck, just 2 weeks apart last fall. The first time, there were large red snapper about, but they remained at the edge of my visibility, and often circled around and came up behind me. As soon as I turned and made eye contact, they bolted. Two weeks later, with red snapper season closed, I was literally poking these same fish in the side to get them to move out of my way for a shot on a grouper.

I doubt that they knew the season was closed. I can only conclude, like everyone else, that I was giving off some subtle clues that caused the red snapper to interpret me as "not a threat".

It reminds me of the old stories of a horse (or dog, or whatever) that supposedly could do simple arithemetic. It couldn't. It was just picking up on extremely subtle signals that the owner didn't even know he was giving.

Nice! I remember when you proposed this idea a while back. Can't wait to see some pics with the bands loaded. Is there any downside?

Is that the 28mm (1.100") diameter barrel, or the 30mm (1.150") diameter barrel?

Sure. What size barrel?

A while back I made some 2-holed muzzles with shark spikes for RA barrles. I got a few requests for a 3-holed version for use with hybrid guns incorporating the RA barrel. So I made a small batch.

These black delrin muzzles fit the Rob Allen aluminum tuna barrels. Holes are 9/16" diameter, and the shark spike is 9/32" spear shaft material. The line wrap pin and line anchor are stainless, and the shark spike projects a little over 1-1/2" from the front of the muzzle.

I have 5 of the plain (no spike) muzzles. The holes on these are staggered for better band lay.

I have 2 of the 3-hole muzzles with a shark spike. Holes on this muzzle are straight in line, because I needed extra thickness on the bottom to hold the spike.

I also have 1 of the earlier batch of 2-hole muzzles left, with spike.

$45 each includes domestic priority mail shipping.

I don't have the anti-gravity ray done yet. In the meantime, you could always use a titanium rod.

I don't see any issues with it. I think that the muzzle extends 1-3/8" into the barrel, in case you intended to put the bolt somewhere other than through the existing holes.

Here's a thought, to keep everything especially clean. The Delrin gets a really good grip on press fit pieces if you drill the hole about 1/64" undersized. If you drill a 15/64" hole all the way through the barrel and muzzle, and then drill out just the barrel to 1/4", you could hammer a 1/4" stainless rod all the way through and it should really stay put. That way, you wouldn't need any nuts or other fasteners on the outside to keep the band elevator in place.

Glad you're happy with it John. Bad day to be a fish.

I put the holes on the tube centerline because I thought that they looked better that way. But there is enough room to raise them slightly. These are 9/16" holes for 5/8" bands, so if you went with 1/2" holes, then they could be raised even a little more.

It says that it can stop the saw in 5 milliseconds after detection. Let's say (just for discussion) that the detection is electrial and so is effectively instantaneous. If you stumbled forward, and your hand or finger was moving at a faster rate of, say, 1 meter per second, then the cut would be 5 mm deep. Nasty, to be sure. But you would probably keep the finger.

I guess the real question is how fast it detects contact.

Some fine teak sawdust mixed in with 2-part 5-minute epoxy will also work, and will match the color about as well as you can without using a teak plug. The thinner epoxy will soak down into the screw hole pretty well.

Drilling the screw hole to the next common size (like 1/4") and using a plug cutter to make a plug from a scrap of teak is probably the most attractive repair (if you care how it looks), but it's never going to be invisible.

Wonder how she feels about honeybees. All those fruits and vegetables pollinated by the unpaid slavery of those poor bees . . .

Sorry, I forgot to take any. Maybe John can provide a few?

Bummer the weather won't cooperate for a test. I think you're going to like the way it turned out. I incorporated Hau's earlier suggestion, and made the line wrap pin just a hair longer, and at a lower angle to help hold the line more securely.