POWER...Pow-wow

[settingsteel]

In the process of powering up my new prototype gun, and have heard quite a few opinions on too much, or too little power and its effect on how the shaft will travel (accuracy)

I have read too much power will cause a low shot, and I have heard the same on to little power

I have also heard the exact opposite- too much=high shot

I have also heard too much power will cause an "arch" in flight

One my protoype guns (as e reference point) is 48" (122cm) total. Distance from band to notch is approx. 39" (100cm). Gun will have a 4 band capacity, band length 14" (36cm) to 16" (40cm). shaft is a 55" (140cm) 9/32" (7mm) riffe...whats the prognosis

 

[Bill]

Tone
A fiew years ago I built a gun very close to that size with a 5/16 (8mm) shaft. Mid handle, no track. I set up a target and increased power until it wouldn't shoot straight. Recommend it as a fun way to learn a new gun.

 

[Pastor]

I would agree with Bill, it's difficult to make recommendations with a home made gun. Certainly with a mid handle if it is over powered it will shoot low because of muzzle lift.

Do you need 4 bands on such a small gun? Wouldn't 3@11x14mm be easier or even 2@11x18mm? (22" total length) Easier to load and a lot less clutter

 

[Old Man Dave]

I have messed about with power versus accuracy by reading a hell of a lot and then building a prototype gun and testing it. I kept it simple by making a single band gun. I discovered several things which may help you at least as a starting point. The 2 main factors seeem to be recoil and spear whip.

If the power is high and the mass of the gun is low then the recoil will tend to kick up the muzzle which in turn catches the tail end of the spear causing a low strike. Ways to avoid this are high mass guns and to some extent handle position and design. Big guns are mainly wood with ballast and in extreme cases bolt on ballast and lead weights.

Spear whip is caused by overpowereing the spear so it contorts as you fire. Ways to overcome this are thick spears and/or tracks. Tracks can be open or closed or occasionally special guides are used (a la Terry Maas). Tracks can be as simple as a groove in the wooden stock or a full plastic insert with sharkfin equipped spear.

My experience with euro guns was as follows. A 90cm ali tube gun with no track, a 6.5mm spear and a 16mm rubber was an accurate gun although not the most powerful weapon. Fitting any larger rubber such as 18mm or especially a 20mm rubber caused it to be hopelessly inaccurate. My prototype gun with an open track on a wooden stock and using a 7mm spear with a 20mm high performance rubber was accurate and a lot more powerful. The cutting edge of euro single band guns is the Omer XXV Gold that I own. The slim carbon barrel has a moulded in track and with a 6.3mm spear and very powerful single 18mm rubber. The trigger is one of the best and it shoots long and straight provided you hold it correctly and manage the recoil. It is right on the limit but suits me.

Hope this helps and good luck with your project.

Dave

 

[sunfish]

Dave, I thought you used a Beauchat gun. What length is the OmerXXV Gold?

 

[settingsteel]

Thanks for the input.

Tone
A fiew years ago I built a gun very close to that size with a 5/16 (8mm) shaft. Mid handle, no track. I set up a target and increased power until it wouldn't shoot straight. Recommend it as a fun way to learn a new gun.

Indeed I plan too, just that by gathering some input I could perhaps eliminate duplicating some of the tweaking, if you will

... Certainly with a mid handle if it is over powered it will shoot low because of muzzle lift.

Do you need 4 bands on such a small gun? Wouldn't 3@11x14mm be easier or even 2@11x18mm? (22" total length) Easier to load and a lot less clutter

Yes, I agree 1 or 2 bands at short distances or at less power. The gun will have the option of up to 4 bands, what I am "playing rocket scientist" at is the elusive short gun/long shot syndrome (trying to get a fairly short gun to give me tuna ballistics:duh(well maybe lil'tuney), the gun is a rear handle (although I have made a few for friends that have been fitted with the beuchat trigg mech, (1) 20mm band and the riffe euro shaft- that are absolute lazers), it is also an enclosed track (up to the last 6" of which it is open-20' shots with fish on...so I have been told).

In paper (actually computer generated design) various concepts have been "neutralized"...these where also noted by OMD (guess in old ways, trail and error, results are same- Thx Dave for the input-the way you explained it makes TOTAL sense to me now). This gun is hvy 8 lams and will always carry 2 shafts, and will have a stainless steel muzzle,yet it seems (on paper) it will still be in need of ballasting, so we're looking at a pretty hvy piece of artillary, theoretically crossing off recoil, as well as the unique design which will lessen vertical movement...the enclosed track also (theoretically on paper) should virtually eliminate shaft whip...

OK that said and the reason for this post is what can 4 (5/8) bands on a 100cm gun really do if all the above is "neutralized" the computer says something that sounds to ridiclous (distance-wise&power) for me to write (at this moment) and says nothing about accuracy at that distance...so where does that put us?

Apologies for the long post

 

[Old Man Dave]

Sunfish

I have a standard 75cm beuchat that I bought new last year for £50 ex vat. I got it for night diving as I needed something simple. It is rigged with a very short line to prevent tangles at night. Also using the standard 16mm screw in rubbers and standard 6.5mm spear. Although intended for night diving I have found it to be a great gun for flatty diving by day and around the reefs. I have even shot a few bass with it. It is actually a joy to use a simple gun and provided the range isn’t too great I seldom miss with it. Used it the other day http://forums.deeperblue.net/680134-post2214.html.

I also own a Maori mamba 90 which is an amazing gun. So powerful yet so little recoil and it’s tiny too. Trouble is I’ve never bothered to get used to it and I find it hard to aim.

My main gun is an Omer XXV Gold 90. Carbon barrel only 25mm diameter with a full built in rail, 6.3mm spear, 18mm super strong rubbers and the best trigger mechanism available. Not an easy gun to use but a very fine weapon with a long range flat trajectory and very light and quick in the hand but also a bit too delicate for rough use. Great for bass both in open water and in the weedy shallows.

I also own a woody with 20mm high power bands. A full rail and a 7mm spear. Bit of an elephant gun but good fun.

Used to own short compressed air guns for use on conger and wrasse etc in the holes but when it fell to bits I didn’t replace it as I don’t fish that way any more.

Dave