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Discussion Starter · #1 ·
Hi folks,
First off, I didn't see a "posting Edicate" thread so if I do something wrong I appoligize. Anyway I got interested in slingshots a couple of months ago and jumped right into it. As is typical for me, I learned all I could in a short time and then skipped all the beginer stages and went straight into an advanced project. Needless to say, I need help.

My project is a slingbow on a gun style frame. I'm using 5/8 black speargun tube. A crossbow with 150 lb. draw wt. and 17 in. draw length can get 300 - 400 F.P.S. My slingbow has 135 lb. draw wt. and 25 in. draw length so I thought I could get about the same. Not so. I get 170 F.P.S. and that stinks

So now I'm thinking I should go with bands. I know the basics on bands and I have found plenty of information on how to cut, mount, and order bands but I haven't found any info on how to design them. How long to cut for a particular draw length, how wide to cut, how much taper, and so on.

So, if anyone has a link or two that you think could help me out, or, if you have any suggestions how I could make this the most awesome arrow slinger in the south I sure would appreciate it. I've put alot of work into this and I would hate to have to throw it away.

Specs:

O.A.L. 46.75 inches
Width 5.5 inches
Wht. 6 Lbs.
Draw Wht. 135 Lbs.
Draw Length 25.5 Inches
Arrow Length 29 Inches
Arrow Wht 395 Grn.
Arrow Speed 170 F.P.S : (

Here are some pics.
 

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No other shooting sport compares.
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170 FPS is pretty good for an arrow! You could kill deer with that. Unfortunately I dont know much to be able to help you. But I look forward to some further tests from you! Welcome to the forum.
 

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Hi folks,
First off, I didn't see a "posting Edicate" thread so if I do something wrong I appoligize. Anyway I got interested in slingshots a couple of months ago and jumped right into it. As is typical for me, I learned all I could in a short time and then skipped all the beginer stages and went straight into an advanced project. Needless to say, I need help.

My project is a slingbow on a gun style frame. I'm using 5/8 black speargun tube. A crossbow with 150 lb. draw wt. and 17 in. draw length can get 300 - 400 F.P.S. My slingbow has 135 lb. draw wt. and 25 in. draw length so I thought I could get about the same. Not so. I get 170 F.P.S. and that stinks

So now I'm thinking I should go with bands. I know the basics on bands and I have found plenty of information on how to cut, mount, and order bands but I haven't found any info on how to design them. How long to cut for a particular draw length, how wide to cut, how much taper, and so on.

So, if anyone has a link or two that you think could help me out, or, if you have any suggestions how I could make this the most awesome arrow slinger in the south I sure would appreciate it. I've put alot of work into this and I would hate to have to throw it away.

Specs:

O.A.L. 46.75 inches
Width 5.5 inches
Wht. 6 Lbs.
Draw Wht. 135 Lbs.
Draw Length 25.5 Inches
Arrow Length 29 Inches
Arrow Wht 395 Grn.
Arrow Speed 170 F.P.S : (

Here are some pics.
something tells me you are not going after squirrels?
 

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maybe try with multiple smaller tubes. when i used to dive alot, our guns had 3 tubes that size. but our shafts weighed about 2 lbs. i think my gun shot about 200-220 fps underwater with bands you'd have to retrofit your system for flat bands- i.e. changing the rollers. i think you should try smaller diameter tubes 2 0n each side before retrofitting it for tubes. you may also be losing speed to friction in the rollers. stick with t, that thing looks amazing!
 

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or just say f#%k it and cut triple 30-20 mm taper bands from thera gold at (draw length/5) and eliminate the pulleys.
 

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I have a Speargun also going to try and make it into a Combow sling took it all apart mine is not as nice as yours but if I have any Ideas I will throw them your way hope you will do the same also. Looks like you would need smaller tubes to get your smoother action but also more control. nice design Keep us posted wecome to the forum .
 

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Your problem is the short draw length. A Crossbow is already pre-stressed, thus it has a high drawing force during the whole shot. Not so your slinggun that gradually decrases its acceleration during the shot. Have a look at existing slingshot-gun designs, they are much larger (and hence much more cumbersome, which is the reason why they never got too popular).
 

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Discussion Starter · #9 ·
Thanks for the replies guys. Lots of good ideas. I didn't think about using multiple smaller tubes. I also didn't think about a string bow being under tension at the begining of the draw. Sometimes I can over look the most obvious details.

I think I'll try the theraband gold idea since I have a piece of it in the garage. So pop shot, how did you come up with the 20 - 30 thing? Maybe I should go with 50 - 30 or something else. how many strips can I use at one time? Is there a rule book or something that tells what works and what doesn't?

Scrambler84 keep an eye on this thread, I'll post how things turn out. work out.

I did not make the butt stock or the scope. The rollers I made from 2 inch nylon stock. They have oil-lite bearings inside them. Very effective. Everything else I made from aluminum stock that I got from work.
 

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See The Target
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There is loss of speed through "hysterisis". Check out bill hayes video and flat bands slang terms and definition post. I know this is only a small part of the problem you experiencng.
 

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http://www.slingshot.../band_calc.html

roughly recomends tripple 3x1.3x160 (cm) bands. the basic underlying logic is that the length of the bands is generaly 1/5 the draw lenght, the width is determined by the required draw weight with a 1cm thick peice of TBG roughly equal to a 1.3 kg (2.9 pound) draw.

The draw lenght of a shot is one of the major factors determining speed, if possible increase this dramaticaly, concitering how good your design is I wouldnt go changing a thing. If possible use lighter ammo.

Dont get your hopes up to high, with this set up 300-400 fps is out of the question but improvment is alwase an option
 

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Discussion Starter · #12 ·
Just thought i'd post an update. I tried three straps of thera band gold 50mm to 30mm. Got about 70 lb. draw and 136 FPS. I'll be going back to the speargun tube. Ill try the 3/4 inch stuff. I'll need to build a crank to cock this thing though. Anyway, thanks for all the help and advice.
After checking out a bunch of cool projects on this site, I had to try my own design . I'll try to get it posted.
 

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That looks gorgeous, but the bands are not going to shoot an arrow as fast as lighter flatbands. In slingshots, more drawweight does not necessarily mean more velocity.
 
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