muzzle design

[scallywag]

hi all, long time reader infrequent poster!. Got into spearfishing last summer and love it. I am an aircraft engineer by trade with access to a range of manufacturing machinery so i thought i'd have a go at a bit of diy speargun making. one thing that puzzles me though, on an open muzzle design gun what keeps the front of the spear in the rail whilst tracking through the water? surely the water pressure/drag would displace it? any input would be greatfuly recieved!

 

[foxfish]

Hundred of post about open muzzles via the search button here is one with pics showing the running line holding the spear in place.... http://forums.deeperblue.com/hunting-equipment/66441-new-rabitech-open-muzzle.html

 

[scallywag]

pardon my ignorance and many thanks for your reply. going to start designing the trigger cassette tonight, draw it up and laser cut it from stainless.

 

[foxfish]

Ok, you might not get much support building your own trigger!
Even the most experienced gun building engineers like Tin Man or Don Paul dont build their own triggers due to availability of fantastic units & for obvious safety reasons.
Sorry if I sound a bit negative as I love gun building myself & I am genuinely interested in any components you build but, as I say triggers usually get loads of negative responses.
I think it has a lot to do with the difficulties of hardening the metal faces?
There are quite a few pictures & stories about folk triggers misfiring around the forum!
On a different note have you seen the hammer head design muzzles - they have band lifters built in that help align the power straight down the barrel.

 

[scallywag]

been thinking about trigger design for a while now. I bought an old gun from ebay with the thought of reverse engineering the mech but when i looked at it, it was so basic i new i could do better. i've got lots of experience of working with aluminium and stainless steel so it presents no problems for me and the linkage is quite simple. will get the trigger sorted then the gun design will follow. will keep you informed

 

[Tin Man]

To your original question, I think I have seen three general ways of holding a spear in place with an open muzzle. The first, like foxfish showed, is to wrap the shooting line over the spear to hold it down. The second is to insert NIB magnets into the muzzle. Just be sure that they are well covered with epoxy because they don't like salt water. The last is to design the sides of the muzzle track so that they partly "snap" over the the spear slightly. Not all the way over the top, but just a little above the midline. I know that I have seen this on a couple of available guns, but I can't remember which ones. I built one once, and I can tell you that you will have to give careful consideration to how the shooting line and crimp get pulled through.