33 replies to this topic

[JoergS]

Hello,

as you may know, I am currently asking my youtube subscribers what they want me to focus on.

Many people want to see slingshots that are powerful, but that have a low draw force so that average guys that aren't weightlifters can handle them.

The key, of course, is shooting smaller ammo. I have focused on the 9,5 mm steel balls (3/8 ") as those are common and cheap.

I started out with Thera Band Gold, cut 23cm x 2,8cm x 1,8 cm, a single band per side. Effective length from pouch to fork is about 20 cm.

That is a very light band with a very easy pull.

It does about 80 m/s, 262 fps.

Then, I changed the band size to 23cm x 4,1cm x 0,5cm - this is exactly the same amount of rubber. And the same pull! With eyes closed, you can't tell which band is on.

Also, I made a very small pouch, just large enough for the 3/8 " balls.

The results are astonishing. 96 m/s, 314 fps! With a band so light a preteen boy can probably pull out.

Next, I will use Thera Band Blue, cut it 23cm x 12,4cm x 1cm. This will have the same draw force as the Blue band is about 1/3rd of the thickness.

Let us see if I can propell the ball beyond 100 m/s!

This is fun.

Jörg

[crazyslingshot]

wonderful tests.
Any video?

[JoergS]

Sure, but I will finish the experiments first.

Jörg

[Brooklyn00003]

Great tests I am too looking forward for a video or two.

[Tex-Shooter]

Joerg, you should be able to get to about 400 FPS! Flatband did and I got 393 Fps. However be very carful, because when bands are stretched to there ultimate limit, they tend to tear length wise and can cut you like a knife. -- Tex

[JoergS]

OK so I did test the blue and black bands, no enhancements. Gold seems to be just perfect.

This real lightweight band set (that a kid can draw), fired from a very simple fork (my Cougar) does 95 m/s or 342 km/h with a 3/8 ball, that would be 311 fps.

And it shoots a lead BB (.177) at 124 m/s - that would be 406 fps!

So far, the Thera Gold did not break, neither did the Black, but the Blue ripped about 2 inches from the pouch.

This has promise. What happens if I do the same tapering to real strong bands?

What I can already say is that extreme tapering enhances the speed much. 1,55 to 1 is almost 20% slower than 8,2 to 1! 30% more energy at the same draw weight.

Next, I will try a "Hunter Band" with a 9:1 tapering (9cm fork, 1 cm pouch). Same amount of rubber as Fish's classical 6 cm fork, 4 cm pouch dimensions.

Man, I love the chrony!

Jörg

[whipcrackdeadbunny]

I thought Gold was the strongest?
Do you think the band length will affect the limits of the taper?
I like the idea of a smaller pouch, I use a really small pouch on my rock throwing sling, it works a treat.
I love Jorgs chrony.
;-)

[JoergS]

Gold is the strongest, that is why you have to cut it in stripes. Usually, blue bands shoot faster than gold because it is thinner (you just have to use wider stripes to get the same draw weight).

I have by now tested the 9cm to 1 cm Gold tapering. Not much faster when shooting the 3/8th, but I did get over 100 meters per second. Remember no draw extension.

With bigger balls, there was no speed advantage over the standard hunter bands. Dramatic tapering works better the lighter the ammo is. Understandable, a few gramms of rubber that you save when you max out the tapering makes a big difference if the ammo weighs a few gramms only - with heavy bullets, the ratio does not matter so much.

I think I pretty much maxed out the 3/8 on Thera Band stuff. It is well possible that the natural latex is a bit faster, but believe me sending the steel along at 95 m/s is impressive. You can't follow the flight of the ball with your eyes anymore.

The bands have by now done maybe 50 shots and are still OK.

If you want to make your teenage boy happy, make him a slingshot with that band setup and give him a bag of 3/8ths. He will love it.

For those who hunt, this clearly is an alternative. Lots of speed and penetration at a draw weight that is so low, it makes aiming easy.

Jörg

[King Cat]

I have a problem. Whenever I see data indicating the velocity of a shot, with little additional data, I get frustrated. For me to make any cense out of it I want to know the size and type of ammo being used. The draw length is also of great value. But – the most often data omitted is the draw weight. To me the draw weight is critical. If I change from a 10 pound draw to a 15 pound draw, my accuracy goes to pot. When draw weight is discussed it is often expressed in relative terms like strong or light. That doesn’t get it because what would be light for someone like Jeorg may be strong for me. It is not that draw is hard to measure; all that is required is a simple fish scale that can be purchased for a few dollars. Place the hook on the scale into the pouch and pull back to where the pouch is at your normal anchor point. Hold it there –turn- and read the value. If you want to spend a little more, get a maximum retaining scale, that way you can relax the draw and read the value at your pleasure.

[ZDP-189]

Why stop at 100? 344m/s is the ultimate goal

[JoergS]

Well, it just happened - the rubber split lengthwise. The 400 fps shots do that.

I was well protected, so no injuries at all, but I have to warn everybody to go that high. The rubber snaps without foreboding, it just rips when you draw out.

I think we need to stop at about 90 m/s for a safety margin.

Jack, I don't have a good scale here, but the draw weight is really, really low. Much lower than the draw weights on the weakest Trumark bands.

Jörg

[ZDP-189]

Tex-Shooter, on 28 May 2010 - 06:18 AM, said:

when bands are stretched to there ultimate limit, they tend to tear length wise and can cut you like a knife

Plus they won't contract as powerfully. If you are at breaking strain, you've gone way past the optimum. Get longer bands; seriously. My blog post of today has graphs that explain this.

Jörg, I'm glad to hear you weren't hurt.

[ZDP-189]

PS, you need a light pouch and light and narrow (waste less elastic) attachment method. I am experimenting with fabric and vulcanising rubber cement.

If your pouch and attachment weighs multiples of the shot weight, a modest reduction could give a real boost in velocity. Here I plotted the speeds you got for different shot weights from Express Bands.



It implies that an empty pouch would go 90 m/s. To continue the example, if you were using express bands, your half gram 4.5mm BB would be pretty close to 90m/s. If you could then shave off 3-4g from your pouch and tying, you'd be pushing 100m/s already. This is just your normal draw without stressing the bands if I remember from the video.

[JoergS]

My tying is already very light, I use thin string and cut off all execess rubber. The rubber is stretched to the max when tying.

The pouch is as thin and short as possible. No excess there.

For me, the 3/8 is too small already.

Shooting bigger ammo clearly means much longer band life. I think that is the secret of my everlasting Thera Blue band set at Alverton - I only shot the big ammo, and did not stretch out all the way. Fairly slow shots with not much energy left after the ball is on its way - no handslap, long lasting bands, powerful shots. That is the goal of optimization.

Jörg

[TruckeeLocal]

I agree with Jeorg, how the pouch is attached is really not the issue. I also agree that 9.5mm ammo is just to small unless all you do is punch holes in paper. This is exactly the reason I've been shooting .395 lead or 7/16 steel. With the right velocity its has a nice flat trajectory for target and packs enough power for hunting. I want one sling that will do it all.

[Tex-Shooter]

Very good comments Joerg! Sometimes I get frustrated because it seems like that some just read in post just what they want to hear. I have had a Crony since 2001 and I would not be without it. It got shot once at the 2003 tournament by some one (I don't know who) while we were eating lunch. It made a dent in the front sheet metal, but it still worked fine. After a couple of months the dent healed its self and the unit has worker fine since also. I have learned a great deal using it. It is a great myth buster. If they were so cheap in the 60's tubes might never got a real foot hold. -- Tex

[Flatband]

Congratulations Joerg, I think you me and Bill are the only ones to ever tear a set of bands lengthwise! You need great speed to achieve this and it is not pleasent when it happens. When I did all my testing the most important things I found out were:

the higher the temperatues and lower the humidity the greater the speed:
As light as possible pouch and attachment:
flat thin latex bands will perform the best:
Super extreme tapers are a waste of time(especilly on thicker gauges of rubber because the front (big end is loaded too much) 2.5 to 1 ratio or maybe slightly higher seems optimum
Very light ammo:
Super fast draw and release-can't afford any hysterisis ( rubber power loss due to holding) when you're speed hunting:
Another thing worth mentioning is to use the frame that has the least pouch drag or band slap a nice OTT or a TTT with a big throat opening (no rubbing):
Finally if you can get a set of bands to last over 20 shots doing over 400fps -Please tell me how! Oh yeah,nice job Bud! Flatband

[ZDP-189]

Flatband that's a superb post. Have some rep.

[JoergS]

Gary, you are right, the 400 fps stuff is simply a band killer. I think we should leave that kind of speed to the air rifle folks.

But still, the experiments were pure excitement! Great fun.

Jörg

[huey224]

hi are u still making the video?
i really want to see it.

[JoergS]

Don't think I will. Too dangerous! Folks may try that at home. I may include the info at a later time, in general terms.

Jörg

[ZDP-189]

Too dangerous for the man who shoots through coconuts?

When you were shooting were you doing it freehand or did you have it in a bench rig?

[JoergS]

I was shooting freehand.

Could not resist and made a setup for BBs. Tapered from 5 cm to 1 cm Thera Blue.

It shoots steel BBs at 137 m/s (449 fps), and a .177 lead diabolo with respectable 123 m/s!

Daisy lists their BB guns at 350 fps...

Rubber rules!

Jörg


So far no lengthwise splitting, but I am well protected.

[Brooklyn00003]

Amazing ! You are shooting single shots yes? Whats the weight of the .177 ?
Thanks

[JoergS]

Yes, single shots with a tiny pouch.

The BB weighs about 0,30 gramms, the .177 weighs about 0,50 gramms.