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Some type of tilefish, I think.

10-4. Thanks for the feedback.

Quote from seahunter49

I feel smart

That happens to me sometimes, but it goes away. <img src= " height="23" srcset="https://spearfishing.world/forum/images/smilies/emojione/1f606@2x.png 2x">

Sorry that they were difficult to install at first, but I like your solution. Was the belt getting hung up because of the thickness, or the width? By that, I mean did you have the edges tapered like this:

If not, then that's obviously easy to fix. You are right in that it is almost impossible to thread the weights if the belt does not protrude through the slot enough to get a good grip. If you were finding that your belt was too thick for the weight slot, then I need to adjust the dimension to better accomodate the RA belt. I check every weight to make sure that it fits easily on my RA belt, but this makes me wonder if maybe the thickness of the belts varies somewhat from one to the other?

One other thing that I should mention for anyone else who may have trouble. It is very hard to hold the weight in one hand and pull the belt through with the other. It works much easier if you put the belt on the floor. Step on the buckle end, and pull the free end to stretch the belt. THEN slide the weight. You probably already figured that out, but it isn't always obvious to someone else just looking at the pictures.

I think you're right about the spike needing to be shorter. It's always easy to cut more off, so I started with it a little longer than where I thought it would end up.

The JBL has larger diameter tube than other railguns that I have seen. The JBL tube is 1.25" OD, whereas most euro guns seem to be 28mm (about 1.10") OD. It's not for me anyway. A few people have inquired about wanting one for their RA guns, so that is what I am specifically interested in. You have a good point about moving the plug, though. If the plug can be driven just a little further down the barrel, then the attachment problem goes away. I would probably use a piece of plastic instead of a wooden dowel, but the same concept.

Dan proposed the idea of a kill spike for railguns to me quite a while back, and I finally got around to building a quick prototype. What's missing, obviously, are the mounting holes to attach it to the muzzle end of the tube. Since I don't even own this type of gun, I need a little advice.

What is the internal plug made of? How long is it? If the attachment screws penetrated the aluminum tube and tapped into the watertight plug, would this cause a problem? Is the plug made out of a hard plastic or other material that might even help hold the screws? Is there enough room between the inside of the muzzle, and the watertight plug, to use nuts or some other piece inside the tube for the screws to bite into?

I would like to use two mounting screws on each side. Possibly the forward ones would tap into the part of the muzzle which is inside the tube. The rear screws would be in the barrel plug area, if possible.

Thanks for any thoughts.

Hmmm. I don't think that it's case hardened. When I welded the tab on Dan's shaft, the heat burned the coating and left a chalky yellowish residue. I have welded hardened gears before, and they left no such residue, presumably because case hardening infuses such a small amount of carbon, nitrogen, or whatever, that there isn't enough to burn and produce any noticeable residue. Case hardening also would provide no corrosion protection.

Ok, then I retract my statement. Perhaps the new coating is some form of galvanizing. But I doubt it.

Dan - Very common in my line of work to take relatively soft piece of steel which is tough and resistant to cracking, and then coat it with something very hard to prevent wear. Chrome is one such coating, as is Boron Nitride (the gold coating on some drill bits). And increasingly, ceramics.

Not sure. It was a darker color, so maybe it was the older coating. Dan?

The hardness tester that I use is called a "micro hardness" tester. It uses a controlled force to push the point of a very small diamond tipped probe into the steel, and determines hardness by how deep the probe goes. We're talking thousandths of an inch. You can barely even see the little spot where the probe was. Most platings are a few thousandths of an inch thick. I noticed that the hardness of the shaft was considerably higher in an area where the coating was intact, and considerably softer where I had belt-sanded the shaft surface flat. It didn't get hot in this area, so I don't think that I softened the steel.

The only other explanation that I can think of is that the sanding may have left the shaft surface rougher when viewed with a magnifying glass, which could possibly have affected the hardness readings.

When I did hardness testing on the shaft that I welded for Dan, I found the coating to be harder than the underlying steel. I don't know what the plated coating is, but it ain't galvanized. Galvanizing is mostly zinc, which is very soft.

I usually order mine from www.mcmaster.com. These are older prices from my catalog, but should still give a comparison.

Black Delrin 1" diameter round bar is $4.04 per foot (8576K21). Square bar is available, but about triple the price. I would just buy a slightly larger round and cut it down if I wanted square.

UHMW is available in round bars, hollow round bars, and square/rectangular bar. 1-1/4" diameter round (white) is $2.40 per foot. 1-3/8 OD by 5/8" ID is $5.60 per foot.

Not saying that those are the right sizes, just a comparison.

I know absoultely ZERO about pneumatics, so I would certainly defer to those that do. But I do have a little experience making things from plastic.

PVC is strong, but a little the brittle side, especially if it is exposed to lots of sunlight. CPVC (gray color) is a little better on both counts.

Delrin is stronger, as well as tougher, and the black color helps resists deterioration in sunlight.

Or, use UHMW. UHMW is not as strong as Delrin or PVC, so a slightly larger diameter piece should be used. But it has extreme impact resistance and toughness, meaning it will bend but not break. And different from PVC and Delrin, UHMW floats, which seems like it might be handy for a freediver. <img src= " height="23" srcset="https://spearfishing.world/forum/images/smilies/emojione/1f606@2x.png 2x">

My gun wasn't quite that large. I think it was about 1-11/16" wide by 1-7/8" tall before shaping. He doesn't do the poured epoxy tracks, but he can do a regular wooden enclosed track. He can also include a short dovetail delrin section about 6" long at the muzzle end to protect the wood track from breaking out if the gun falls over or something strikes the shaft. I should also clarify that the prices I mentioned are just for the stock, with a 1-1/2" wide by 2" tall stock going for around $150. Tracks, trigger pockets, tapering, and other cutting/machining are all possible, but cost extra.

He is not really out to build guns. We just noticed that laminating the stock and then aging and staightenning were the parts that most people would prefer to avoid, and are MUCH easier with the right tools. His stocks are all hung vertically, aged, and guaranteed straight to within 0.015" on top and sides, and usually they are closer to 0.010". This way, when you get your stock, it's time to start the fun part!

I'll start a thread in a bit, but here are a few pics of my stock. He makes laminated stocks to whatever size you want, with laminations usually about 3/8" thick. Most stocks range from $130 to $180 depending on the size. All Burmese teak, and laminated under pressure with West Systems epoxy.

Will do.

Dad can also provide dovetailed Delrin enclosed tracks. Very tough material, but cuts and finishes much nicer than UHMW. It's a little heavier, though.

If you look carefully, you will notice that the right side of the sectional drawing shows a screw inserted, while the left side shows an empty hole for reference. :poke:

I saw the thread. That's what got me thinking about it!

I was thinking about this recently as well, Dan. <img src= " height="23" srcset="https://spearfishing.world/forum/images/smilies/emojione/1f606@2x.png 2x"> Here is the drawing I made. No significant differences, really. I drew it with the intent that the attachment screws would bite into the section of the muzzle which is inside the barrel. I also designed this sketch with very little "wrap" around the barrel, so that it could easily be installed off to one side to provide clearance for the shooting line on the other side. That might affect balance, though, depending on how heavy the spike was.