Euro-Hybrid R&D Project

[Old Man Dave]

I've built a new gun to use as an R & D tool. I'm setting out to produce a 90cm euro style gun using a set of 20mm screw in rubbers. Test spear is 120cm x 7mm diameter with a screw on head. Trigger/handle is Immersion 2 stage and head is beuchat. Stock is one piece mahogany with full length rail and built in wings.

The aim is to try different spears, spearheads, rigging, line sliders and rubbers as well as different weighting using a very sturdy sock. I'm looking for maximum flat spear trajectory with minimal recoil.

Results will enable me to build another gun based on the findings. Final gun may well have a wood handle and more refined trigger. R & D gun is currently just finished in epoxy to provide some protection but once tested/modified the eventual finish will be cammo.

Dave

[Old Man Dave]

More pic's

[Mr. X]

V.cool Dave - although I am surprised that you went for a fitted muzzle rather than fashioning a bulk-rubber hole up front. I read an article when I first starting looking into spearfishing by a spearo in Taiwan -- apparently they usually swap out the barrel of euro-guns & replace them with wood (not sure how elaborate - I doubt they have rails & wings like yours though!).

Seems a shame to camo mahogany. Perhaps a subtle desert sunburst in nitro-cellulose?! (Like a fine guitar).

[poacher]

[quote=Mr. X]V.cool Dave - although I am surprised that you went for a fitted muzzle rather than fashioning a bulk-rubber hole up front. I read an article when I first starting looking into spearfishing by a spearo in Taiwan --
Dave ,Im with Mr X on that I;d have gone for the bulk rubber muzzle cheaper up front and also down the track if you make your own rubbers.
Mr X do you stll have a copy of the article from Taiwan? I would love to see it.
Peter

[Old Man Dave]

I've done some testing of my gun.

First up I balanced it. Eventually it took 1 oz in the nose and 3 oz's in the handle to get it just floating horizontal fully rigged. It now weights 4lb exactly (1.7kg) in air.

I first rigged it with a single wrap of 160lb mono with a slider (slip ring) which gave a range stop at 9ft. This was not enough. The first firing saw it reach the end of the line with a mighty tug which I could see was gonna cause damage. Re-rigged it with a double wrap plus slider which worked out at a full stop at 14.5 ft. It reaches the end of the line with a good tug still. Was impressed by this. Couldn't tell the drop at full range but doesn't seem to be more than a foot maybe 18 inches.

Test fired it at a target, in the sea, in about 3 ft of water, just hand held. Typical shallow water hunting conditions. Turned out at 8 ft (2.4m) or 2 spear lengths it was on line but 2 inches low. Reversing the screw on flopper head improved this to about 1 inch low. At 6 ft it was spot on (flopper below). Some of this could be my aiming as it was as I said hand held. However for an initial test I was well pleased.

Recoil was very low and absolutely miles better than my "standard" euro when it had 20 mm bands. Accuracy I thought was better than I could have hoped for, for a first try.

Next step is to re-rig with a 6.5 mm spear and no slider and re-test.

I have also shot a few fish with it and it feels good but more testing, both on targets and fish is my plan.

Dave

Have attached a peper copy traced from my target. Scale marks are inches.

[Dan Man]

I dare say the slider on the spear is causing the inaccuracy. Those things are horrible! Once rigged with a single wrap with the mono going through the hole at the back of the spear should fix it right up. Single flopper...can't get much more accurate!

[Mr. X]

Hi, saw this page the other day: http://www.beuchat.fr/catalogue/inde...egorie&scat=13
The cross section of the Mundail Carbon Elite, with the wings & rail reminded me of yours:
Do you like loading butts? Seems like a good idea - you need a decent loading pad with my railgun - but would it interfere with aiming along the side of the barrel?

BTW my railgun has a 90cm barrel (tube measured end to end, inc. the part inside the handle & muzzle) too & the standard spear it comes with is 6.6mm x 130cm i.e. barrel length + 40cm. SA railguns usually have the barb on the bottom. [BTW you can get spears from RA in the UK for around 14 pounds, with a holed drilled in the rear. They offer a universal-style for non-RA spearguns. Various lengths & diameters. I notice Portland Oceaneering offers spears from various makers. Oh...I forgot...you probably make your own!]

[foxfish]

Originally Posted by Dan Man

I dare say the slider on the spear is causing the inaccuracy. Those things are horrible! Once rigged with a single wrap with the mono going through the hole at the back of the spear should fix it right up. Single flopper...can't get much more accurate!

Interesting comment Dan, I have heard this mentioned many times before. I have carried out my own test with sliders & found them very good! Certainly works on my mamba air gun! We will be testing Dave's gun with different combinations of spear, line, sliders etc. There is no knowledge that beats first hand.

[spaghetti]

Dave, I like your speargun very much. I'm sure a perfect accuracy will follow after the improvements you will try (no slider, etc.), as I see you determined to finish the job at a state of the art level. Let us know the results of the next testing.

PS- About Mr. X's question, loading pad can be a good thing for aiming purposes: a valued speargun builder (Valerio Grassi) says that yes, the loading pad covers the view of the shaft, but this way you're forced to lift the muzzle a bit while aiming, and this helps. Because he says that rubberguns in general don't shoot straight to the target, but with a slightly descending trajectory. Thus, lifting the muzzle a little bit can prevent low shots.

[Mr. X]

Originally Posted by foxfish

...I have carried out my own test with sliders & found them very good! Certainly works on my mamba air gun! We will be testing Dave's gun with different combinations of spear, line, sliders etc. There is no knowledge that beats first hand.

Interesting. I heard similar stories, all in relation to JBLs (and/or possibly Seahornets/A.B. Billings) spearguns. Perhaps the make has more to do with it than anything. Somewhere on the forum there are details of a modification that is commonly made to fix/improve things (I think it might involve a pin or bracket at/near the muzzle to keep the spearline in order?). Can't find the info. now, perhaps on a different forum. Sounds like you have no such issue though.

[Old Man Dave]

Been doing some more testing. Fitted my 140cm x 6.5mm diameter spear in place of my 125cm x 7mm diameter spear. This spear was now rigged with 160lb mono to the rear hole rather than with a line slider. This was the set up from my original Beuchat gun and the one which was so inaccurate when I fitted 20mm rubbers. So I was keen to see if my new wood hybrid stock with rail would sort out the problem. Bear in mind that the hybrid with the 7mm and line slider + 20mm rubbers was within 2 inches at 8 foot.

Right, well results were crap. At 8ft the spear hit 9 inches low and 1 inch left. Just about the same as the beuchat. Even at 6 ft and with the rubber on the front notch it was 6 inches low and 1 inch left. Hopeless for hunting.

So what's going on. Well I think Foxfish might be right about the line slider. It doesn't seem to be the problem. The 6.5mm spear doesn't seem to handle the power of the 20mm bands. Also the Mamba, as Mart mentioned, uses a line slider and is very accurate. However next step will be to target shoot both spears with no line and see what the results are. Will need to find somewhere suitable so I don't loose the spears.

All this got me thinking and so I decided to test the flexibility of both spears. De-rigged them and in my shed set them up spanning 2 concrete blocks. I hung a 4lb weight mid span and measured the deflection. I was really surprised at the result. The 7mm diameter spear bent 2.5cm while the 6.5mm diameter spear bent nearly 6cm. Even under its own weight the thin spear bent noticeably where as the thicker spear was dead straight. Incidentaly I checked both for true as I could hardly believe how innacurate the 6.5 had been. Both were good.

Need to try the no line target shoot to definitively sort out the line slider issue but what I'd really like is to try a 7mm spear without a line slider but rigged with a rear hole. Unfortunately my 7mm spear is not equipped as such so maybe have to get the drill out.

Dave

Had a further though that maybe some spears are stiffer than others irrespective of diameter. Ed's got a big selection of fancy spears so maybe I can test some of his?

[portinfer]

Hi Dave - glad you made it back from the US of A - think that 7mm is the way to go for punchy guns - would hate to measure the deflection on the 6mm 115cm spear in teh 80cm teak gun ! But I guess it is a bit lighter and the 16mm rubbers or whatever they are work ok.

You can get different results with the band stretch too...

THis is the formular (I know that you have less control over this but might be a future test ?) :

(Stretch length x 2) / 3 to 3.5 = length of rubber

Put 3 for long rubber or 3.5 for bomber setups...

(Centre of hole to back notch - not sure if this is to the end of the rubber or to the end of the 4cm wishbone ? Anyone got clues ?)

(79x2)/3= 52.7 longest setup
(79x2)/3.5 = 45.1 shortest setup

More testing Dave ! Catch you soon - Ed

[Mr. X]

OMD, there are also a couple of tables out there for bulk rubber lengths for railguns. There is a copy of the Rob Allen rubber length table at the Norcal site: http://www.norcalfreedive.com/catalog/bands6.htm

There is similar data here: http://www.homepages.paradise.net.nz...ulk_rubber.htm

There used to be a nice Rabitech chart that showed the recommended range of lengths for 16mm & 20mm rubbers for each common barrel length. I am afraid I just cannot find it anymore - Rabitech, Sumora & Adrenaline have all changed their websites (& not for the better I fear ). Pity, it was a useful chart. Maybe Miles knows where it can be found?