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Muzzle magnets - size?

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Mr. X

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I'm thinking of adding a small magnet to the open muzzle on each of my spearguns to help locate and hold the spear in place during loading. I see that several manufacturers already do something similar, including Beuchat on the Marlin and Cressi on their Geronimo model. I wondered if anybody else has done this and, if so, what size magnet was used?
 
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Mr. X

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I already have a lot of 5mm long X 5mm diameter magnets but they seem a little too strong to me. BTW My 6.3mm stainless steel spears are magnetic, I think not all stainless steels are though(?).

You can get magnets now in almost any size. I'm thinking, perhaps something like 1mm X 3mm diameter perhaps. Other options are 0.5mm X 3mn (could potentially stack these up so, if one is not enough could try 2 or 3 magnets in a stack of 1mm or 1.5mm) , 1mm X 2mm diameter or 0.5mm X 2mm - again these could be stacked to adjust strength.
 

Kodama

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Ideally the power of the magnet should be sufficient to hold the shaft in place when the gun is held upside down.
Mind you that magnetic force slightly decreases in water.
 
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Andrew the fish

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I always thought if stainless could take heat treatment (like spear shaft are) it would be magnetic. If magnet is too strong, seat it deeper by couple mm’s.
 
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Mr. X

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Ideally the power of the magnet should be sufficient to hold the shaft in place when the gun is held upside down.
Mind you that magnetic force slightly decreases in water.
I was just looking for a little help securing the spear while I wrapped the spearline over my open muzzle. With a magnet that strong (5x5mm?), It might be possible to forgo hooking the spearline over the spear to hold the spear in place at the muzzle entirely. That would be a game changer, if would make loading significantly faster and easier! Is that what you had in mind Kodama?

Is that what manufacturers are doing, e.g. Cressi with their magnetic Geronimo muzzle, I wonder? Might cause too much drag in the spear when you fire it. On the other hand it would likely keep the spear gliding through the muzzle guide.
 

Mr. X

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... With a magnet that strong (5x5mm?), It might be possible to forgo hooking the spearline over the spear to hold the spear in place at the muzzle entirely. That would be a game changer, if would make loading significantly faster and easier! Is that what you had in mind Kodama?

Is that what manufacturers are doing, e.g. Cressi with their magnetic Geronimo muzzle, I wonder? Might cause too much drag in the spear when you fire it. On the other hand it would likely keep the spear gliding through the muzzle guide.
Yes! That's exactly what they are doing. :)
 

Kodama

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I have been contemplating the idea of muzzle magnets for a while but I think that wrapping the line over the shaft will remain mandatory. I would not want to rely on just magnetic force to keep the shaft in place.
 
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Mr. X

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My 5x5mm magnets seemed a bit big & powerful. So I bought some 3 x 1.5mm disc magnets but they seem tiny. Powerful though.

Ordered a Cressi magnetic muzzle, might be able to see what they use.
 
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Mr. X

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I have quite a collection of small, strong magnets now:
PHOTO_20200216_145657.jpg

I thought I'd try adding one of the tiny 3mm diameter x 1.5mm depth ones first. They're the ones taped to a warning card on the right ("do not swallow"). They don't need much of a hole.

I drilled a small hole in the compact plastic muzzle of my much loved Omer XXV 90 speargun with a 3mm drill bit in a hand-drill. The small silver dot in the muzzle below is the tiny magnet.
PHOTO_20200216_144805.jpg

I've used UHU glue to hold the magnet in place, so probably not permanent at this stage. I'll see how it works out. Might try a longer magnet if this proves too weak. Otherwise will probably fix with superglue, or possibly epoxy for a permanent fix.
 
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Mr. X

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BTW This is the Cressi Cherokee magnetic muzzle.
PHOTO_20200216_165737.jpg

The powerful magnet:
PHOTO_20200216_171625.jpg

... appears to be under the little rectangular cover in the middle of the muzzle, in image below:
PHOTO_20200216_165941.jpg

Note, the muzzle includes the normal "horns" to allow the spearline to be used to secure the spear.
 
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Andrew the fish

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so when muzzle magnets installed, you don't need to lash the shaft anymore? Or is it just an aid to hold the shaft while loading?
 

foxfish

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Things change but when I experimented with magnets I did not find much success.
I tried using single and mutable magnets both near the muzzle and down the whole barrel.
I think different grades of spears have some effect depending on how magnetic they are and obviously the magnet strength plays a big part too.
The magnets I used were very prone to rust so I had to coat them with epoxy again effecting their effectiveness .
Overall I found the magnets were useful but no substitute for firmly holding the spear in place, abrupt downward tracking would dislodge the spear as would catching in weed so manual attachment was necessary.
However that was 6-7 years back so magnets might have become stronger.
 

Mr. X

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Yes, the rare Earth magnets I use are available in at least 2 strengths. I think mine are probably the weaker ones but they are quite strong.

It turns out that the tiny magnet above, 3mm diameter x 1.5mm, is way too weak for the long spear on my 90cm speargun. At best, it might help locate the spear and help keep it there just a little bit. I estimate that it would likely need at least 4x the holding power just to properly help locate and help retain the spear; it would likely need a lot more to replace the spear line crossover, which I suspect would be impractical for my compact muzzle and superlight speargun. It is not my goal to replace the spearline crossover, I don't think it would be practical for my set up. Electo-magnet?! :D

I could stack several 3mm disk magnets but I also bought some 3mm diameter X 6mm cylinder magnets. So, like 4 disk magnets on top of each other,; see photo of my magnets above. A cylinder magnet will likely be the next thing I try. I suspect it will not be enough. After that, maybe 1 or 2 5mm diameter X 5mm magnets?

Rust, I hadn't thought of that. These are rare earth magnets - do they contain a lot of iron, like traditional magnet?
 

Andrew the fish

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I must say that an enclosed track does the same job, making a reload a breeze, almost as quick as pneumatic gun. ET flooding @ffects the shaft speed though, but it eliminates the whip. Comparing ET to magnet, does magnet at least attenuate the whip to some degree? How does magnet affects the shaft speed? Will be interesting to have side by side pool tests, slo-mo etc.
 
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