# Theraband And Ammo Speed Results



## -SRS-45-

Borrowed a chrony off the local archery club to test out different band sets and ammo type speeds... thought someone else might also find it useful so heres the results.

Its worth noting pulling power, the tbb was easy to draw, the tbg single was okay but a bit of a strain at the length I was pulling, the theraband gold was uncomfortably heavy.

My dad noticed sometimes when I wasn't concentrating I was letting my draw arm creep in just before release, this was loosing me about 10fps which may show up on some of the results which is why I've also included a fastest speed result to remove that.





  








speed table




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-SRS-45-


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Aug 4, 2011


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4


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## -SRS-45-

oh, the theraband black was butterfly style, single theraband gold was anchoring past the back of my head... as far as I can pull. Double theraband gold was possibly up to my jaw... as far as I could pull.

For me the butterfly style won on the overall of speed and comfort though it wasn't as fast as I expected, I may adjust it to 24-14mm tapper (from 22-16mm)... anyone think that will give any better results??


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## Guest

Those measurements are very disappointing. I would have expected the ammo (9.5mm) to fly a whole lot faster than only 1 meter/second on average when comparing TBG single to TBG double. I mean, that completely defeats the purpose of a much thicker, much harder to pull band with decreased accuracy. Honestly, I don't have a Chrony myself (yet) but if I would shoot double TBG, I would expect at least 20-30% more power (speed) - or is this unrealistic?

Thanks for taking the time and bring this schedule up, it is always very interesting to see such results and help to make decisions what kind of rubber might be best for personal needs. I think that I'm mainly going to stick with my 1842 and 1745 tubes. Plenty of speed for me, (almost) endless rubber lifespan and so very easy and quick to attach (both fork and pouch).

cheers


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## -SRS-45-

Yeah with double thera gold I think you gotta have a good pair of arms which I don't have these days. The single thera gold I could get a lot longer draw lengh which helped keep the speed closer.

What I can say on the difference in speed though is when I did my vid for blowing up pressurised cans the single thera gold wouldn't penetrate whilst the double did. The downside of course is that double thera gold cannot be used for shooting lots of shots due to the weight whilst single you can shoot all day


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## NightKnight

Very nice test! I am rating this topic a 5 out of 5!


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## kobe23

E=mc² said:


> Those measurements are very disappointing. I would have expected the ammo (9.5mm) to fly a whole lot faster than only 1 meter/second on average when comparing TBG single to TBG double. I mean, that completely defeats the purpose of a much thicker, much harder to pull band with decreased accuracy. Honestly, I don't have a Chrony myself (yet) but if I would shoot double TBG, I would expect at least 20-30% more power (speed) - or is this unrealistic?
> 
> Thanks for taking the time and bring this schedule up, it is always very interesting to see such results and help to make decisions what kind of rubber might be best for personal needs. I think that I'm mainly going to stick with my 1842 and 1745 tubes. Plenty of speed for me, (almost) endless rubber lifespan and so very easy and quick to attach (both fork and pouch).
> 
> cheers


I believe the difference is not significant because 9.5mm steel is considerable light ammo. Much more energy is transferred efficiently in the lead shots.


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## Guest

kobe23 said:


> I believe the difference is not significant because 9.5mm steel is considerable light ammo. Much more energy is transferred efficiently in the lead shots.


Well, lead gives you about 45% more power during impact because of 45% more weight, but it still wouldn't be different regarding the speed double vs. single TBG.

cheers


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## -SRS-45-

NightKnight said:


> Very nice test! I am rating this topic a 5 out of 5!


Cheers dude


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## kobe23

I see significant difference in speed for lead, don't you?


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## Guest

-SRS-45- said:


> What I can say on the difference in speed though is when I did my vid for blowing up pressurised cans the single thera gold wouldn't penetrate whilst the double did.


There are only two ways to increase power - speed and the weight of ammo. If you used the same ammo blowing up those cans, than there must have been a signifant increase in speed with double TBG, but this is contrary to the measurements you took.....









cheers


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## -SRS-45-

Hmm can't remember, it was pretty close quarters when I did the can video as there was a wall behind me maybe I was only able to pull the single as far as the double. That would have drastically decreased the speed.


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## Guest

kobe23 said:


> I see significant difference in speed for lead, don't you?


Yes sorry, i just have lokked at the 9.5mm steel because usually I don't shot any bigger and heavier ammo. With the .44 lead ball there was a difference of 10meters/second, which is still not overwhelming but at least significant. Not sure what exactly causes the difference to the lighter 9.5 steel ammo though, maybe the stronger bands can simply handle the inertia in masses of movement better....









cheers


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## kobe23

I'll tell you why later, gaming now >.<


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## jskeen

Guys, a little basic physics here might explain some of your results. Any given elastic has certain intrinsic characteristics that are simply part of its internal structure. One of these is the retraction speed. It is something that is just intrinsic to the type of rubber, and it is the maximum speed that the elastic will return to it's original size IF NOTHING IS SLOWING IT DOWN. Now there is always some intrinsic resistance due to the shape of the rubber, with a thin narrow ribbon being about the fastest. But no matter how you cut shape or taper it, it's only going to retract that max speed minus the total resistance it encounters. Thus, Some elastics are faster than others, by nature, and nothing we do to it is going to change that fact.

Now, the shape of the rubber, the thickness and length, and how far it is stretched all effect how fast it will throw a projectile in a slingshot, but it is not going to go any faster (or really even really close to) that theoretical retraction speed. The factors that we do have control of are how long the piece is, how far it is stretched, and HOW MUCH WEIGHT IT HAS TO MOVE. The first two get rolled into the "percentage of elongation" tables that have been published somewhere before. Bottom line there, you want to stretch the rubber right up to it's "saturation point" or that place where you feel it get a lot harder to pull without moving it very much. Anything less, and you are not getting the maximum acceleration out of it, and more than that yields very little extra speed, but decreases band life a lot.

The third factor is the most important, how much weight are you accelerating for a given amount of elastic. The total weight you are accelerating includes the projectile, the pouch and to a lesser degree, the part of the band that is closer to the pouch. Now when working with a strip of elastic within the reasonable size range for a slingshot band, there is a weight to speed curve that is pretty consistent across most different elastics. That curve is pretty flat up to a certain weight, then it starts to drop off rapidly as the weight increases. By using more elastic, either wider bands, doubling them up, or whatever, you can push that drop off point out for heavier and heavier weights, BUT YOU ARE NOT REALLY INCREASING THE INITIAL SPEED MUCH IF ANY. In fact for really light ammo, heavier bands can get in their own way, so to speak, and actually shoot slower than thinner lighter singles. Now all of that assumes that you are maintaining the exact same percentage of elongation!!!!!!! If you stretch the heavier bands less than the lighter ones, especially with light ammo, you will lose projectile speed, sometimes a LOT. The payoff for heavier bands, as you might imagine, is that they can maintain that high projectile speed with HEAVIER ammo, IF YOU CAN MAINTAIN THE ELONGATION.

I have been working on my chrony test jig so that I can clamp bands to a fixed point and then stretch them to a repeatable length, and measure the speed. I'm hoping to get some time to work up some curves for a given set of bands drawn to a certain length, with a series of different weight projectiles and demonstrate that the speed will remain pretty much the same up until you get to a certain weight, then drops off. Then by using all the same factors but doubling the bands, I will bet that the initial speeds are very close to the singles, until you get up to that projectile weight where the speed of the singles started falling. The doubles should maintain that speed up to a much heavier projectile, all else remaining the same.

Of course at the rate things are going around here between work, family and other ongoing and emergency projects, I may die before I get to try it. But if I do get a round tuit, I'll be sure and lot you guys know how it goes.

James


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## NightKnight

Well said jskeen, well said.


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## Guest

jskeen said:


> But no matter how you cut shape or taper it, it's only going to retract that max speed minus the total resistance it encounters. Thus, Some elastics are faster than others, by nature, and nothing we do to it is going to change that fact.
> 
> Now, the shape of the rubber, the thickness and length, and how far it is stretched all effect how fast it will throw a projectile in a slingshot, but it is not going to go any faster (or really even really close to) that theoretical retraction speed. The factors that we do have control of are how long the piece is, how far it is stretched, and HOW MUCH WEIGHT IT HAS TO MOVE. The first two get rolled into the "percentage of elongation" tables that have been published somewhere before. Bottom line there, you want to stretch the rubber right up to it's "saturation point" or that place where you feel it get a lot harder to pull without moving it very much. Anything less, and you are not getting the maximum acceleration out of it, and more than that yields very little extra speed, but decreases band life a lot.


Just to make sure I understand you correctly: Tapering bands do not increase the speed, it's only good for an easier draw but actually worse for shooting heavier ammo (because of less rubber)?

cheers


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## Jimmy

Good work.
A 38" draw on the 8" double theraband gold is pretty good going, I doubt if there was much more to be had.
It would be interesting to see a speed comparison with different sized pouches on the same sized bands, to see if there is much of an air-brake effect.


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## Northerner

Thanks for posting the velocity data. I tried TB-Silver with a butterfly draw and was getting about the same as you were with a slightly wider TB-Black.

Theraband Silver - measurments 3/4" x 9/16" x 9 3/8" - butterfly draw (approx 53") - *230 fps* with 3/8" steel & *255 fps* with 5/16" steel.

Cheers,
Northerner


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## -SRS-45-

Cheers James for the info.

Jimmy: yeah that would be pretty good to see, its all the little tweeks that give an overall great improvement, I'd like to get some of that light weight roo leather to shoot with but seems to be hard to get.

Northener: Yeah thats a good speed, I'm enjoying the butterfly shooting, from the results though I think I need to tweek it a bit to handle the heavier ammo's, though they are acceptable speeds.


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## GameKeeper

thanks for sharing


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## jskeen

E=mc² said:


> But no matter how you cut shape or taper it, it's only going to retract that max speed minus the total resistance it encounters. Thus, Some elastics are faster than others, by nature, and nothing we do to it is going to change that fact.
> 
> Now, the shape of the rubber, the thickness and length, and how far it is stretched all effect how fast it will throw a projectile in a slingshot, but it is not going to go any faster (or really even really close to) that theoretical retraction speed. The factors that we do have control of are how long the piece is, how far it is stretched, and HOW MUCH WEIGHT IT HAS TO MOVE. The first two get rolled into the "percentage of elongation" tables that have been published somewhere before. Bottom line there, you want to stretch the rubber right up to it's "saturation point" or that place where you feel it get a lot harder to pull without moving it very much. Anything less, and you are not getting the maximum acceleration out of it, and more than that yields very little extra speed, but decreases band life a lot.


Just to make sure I understand you correctly: Tapering bands do not increase the speed, it's only good for an easier draw but actually worse for shooting heavier ammo (because of less rubber)?

cheers
[/quote]

That is a simple question with a short answer and a ton of technical reasons behind it. The short answer is No, tapered bands will shoot a little faster than a rectangle band with the same total amount of elastic, as long as you are within the best ammo weight range for those bands. Part is that the part of the bands doing the most movement is lighter than the part that is doing the heaviest work. Another part is that the taper changes the response curve of the band as a whole.

But you do get much fewer shots with tapered bands, and the more taper the faster they will break. The good thing is that they break at the pouch end where it does the least damage.

That's a big part of the fun is playing around with different bits.


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## bullseyeben!

E=mc² said:


> Those measurements are very disappointing. I would have expected the ammo (9.5mm) to fly a whole lot faster than only 1 meter/second on average when comparing TBG single to TBG double. I mean, that completely defeats the purpose of a much thicker, much harder to pull band with decreased accuracy. Honestly, I don't have a Chrony myself (yet) but if I would shoot double TBG, I would expect at least 20-30% more power (speed) - or is this unrealistic?
> 
> Thanks for taking the time and bring this schedule up, it is always very interesting to see such results and help to make decisions what kind of rubber might be best for personal needs. I think that I'm mainly going to stick with my 1842 and 1745 tubes. Plenty of speed for me, (almost) endless rubber lifespan and so very easy and quick to attach (both fork and pouch).
> 
> cheers


Layers will only help ACCELERATE a heavy shot faster than single layer there for giving it a chance to quickly gain momentum, light ammo single layer will prob troavel similar speed minus hand slap and band wear...


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## Tex-Shooter

The chart shows speeds at respectable stretch ratios. It is a great chart! If you shoot ammo small enough to shoot faster than 200 FPS with common pull weight bands, you are losing a lot of the power (foot pounds energy) your slingshot is capable of. If your set-up is too fast you also lose band life.


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## justplainduke

I was calculating joules of energy (randomly from your fps and ammo), which is really the final step that you need on your spreadsheet, because speed without mass is only part of the equation. Pm me on Monday and I will send you the actual mass and info on calculating ft lbs and joules. To a hunter that's most important. Good work!


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## -SRS-45-

justplainduke said:


> I was calculating joules of energy (randomly from your fps and ammo), which is really the final step that you need on your spreadsheet, because speed without mass is only part of the equation. Pm me on Monday and I will send you the actual mass and info on calculating ft lbs and joules. To a hunter that's most important. Good work!


Cheers buddy. I meant to ask if someone could do that


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## Tex-Shooter

http://www.airhog.com/convert.htm


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## -SRS-45-

Great link thanks man. So the slowest (11.1 lead) packs the most punch. Good show


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## -SRS-45-

So in theory if I cut my butterfly bands (currently tappered 22-16mm) to a thicker 24-18mm they will handle the 11.1mm lead better?


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## Tex-Shooter

Yep, but maybe not as much as you might think! -- Tex


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