# New Benchmark In Band Efficiency?



## Setarip (Mar 27, 2012)

Hello!
So for the last few days I have been experimenting with micro bands, and seeing what kind of velocities I can achieve with 7.5mm steel balls. Here are my results:

Non-tapered set: (3/4" straight, 4" cut. 10-12" draw, 41 degree F ambient Temp):
1: 155.8
2:166.6
3:168
4:155.8

Average: 161.55 fps

Bandset one (5/8"X1/4"X4", 12.1 grain rawhide pouch, 10-12" draw, 48 degrees F ambient temp):
Shot 1: 167 fps
Shot 2: 164.6 fps
Shot 3:172.1 fps
Shot 4: 172.6 fps
Shot 5: 172.8 fps
Average: 169.82 fps
Joules:2.75
Peak Joules:2.84 joules

Bandset two (3/4"X1/4"X4", 3:1, 3.6 grain pouch, 10-12" draw, 52 degree F ambient temp):
Shot 1: 182.8
Shot 2:184.3
Shot 3:186.3
Shot 4:195.8
Shot 5: 193.5
Average: 188.54 fps **This is the benchmark I hit, the bandset including pouch and pouch ties weighed in at a total of 31 grains!!! The 7.5mm steel ball weighs in at 32 grains!*
Joules:3.38
Peak Joules: 3.65

Bandset three: (1"X1/4"X4", 4:1, 4.2 grain pouch, 10-12" draw, 52 degree F ambient temp):
Shot 1: 222.5
Shot 2:204.3
Shot 3:198.3
Shot 4: 217.8
Shot 5: 204.6
Average: 209.5 fps (Sadly this bandset weighed in at 41 grains)
Joules:4.18
Peak Joules:4.71

The high efficiency bands were quite a surprise! Had this been during the summer the velocities would have averaged much higher for all three sets. I think that going with this set(set number 2) you can achieve above 200 fps consistently on warmer days, and I put more than 30-40 shots through this without any noticeable degradation(unlike the last 4:1 set which tore after approx. 30 shots) I would like to see others who have Chrony's try and achieve efficiency's like this, and post the results! It doesnt have to be 7.5mm steel, just make a bandset that weighs less than the ammo your shooting, and post your results! Thanks for looking!


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## Henry the Hermit (Jun 2, 2010)

Thank you for he tests. All fresh knowledge is welcome. I have a question or two.

What rubber did you use?

Have you done any scaling tests? By that I mean what happens if you cut a bandset to a more practical working length? A 3/4x1/4 taper at 4 inches is a completely different profile than a 3/4x1/4 taper at 8 inches.

An observation. I think the low stretch factor is the reason bandset 2 survived very long. Most consider a 2:1 taper as right on the edge of extreme.


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## Setarip (Mar 27, 2012)

Figures I forgot an important bit of info! I am using .03" hygenic latex.

The difference in profile is a good point. My goal with these experiments is to hit the highest velocity I can with the least amount of rubber.
I also found out that reducing pouch weight has a large effect on velocity as well...to a point. The differen from 12.1 grains to 5.6 grains was noticeable. I saw about 10% more velocity with the 7.5mm steel. I further reduced weight to 3.6 grains but saw no noticeable increase. I would like to do further research on these!


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## Hrawk (Oct 25, 2010)

Nice work.

I've always been an advocate of lightweight, minimalistic pouches.


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## Henry the Hermit (Jun 2, 2010)

Setarip said:


> Figures I forgot an important bit of info! I am using .03" hygenic latex.
> 
> The difference in profile is a good point. My goal with these experiments is to hit the highest velocity I can with the least amount of rubber.
> I also found out that reducing pouch weight has a large effect on velocity as well...to a point. The differen from 12.1 grains to 5.6 grains was noticeable. I saw about 10% more velocity with the 7.5mm steel. I further reduced weight to 3.6 grains but saw no noticeable increase. I would like to do further research on these!


That bit about pouch weight squares well with my experiments. So far, the lightest leather I've found that will stand up to high velocities is kangaroo.

I believe you will find much higher velocities if you increase stretch factor to about 6:1 instead of your current 4:1. At the extreme tapers you are using, don't expect much band life, though.

Please keep us informed about your experiments.


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## Setarip (Mar 27, 2012)

So I wanted to see what gains there were with a tapered set over straight cuts. I put the results in the first post. I only have 4 readings as I ran out of 7.5mm steel after that









Overall if we compare 3/4" straights to 3/4" tapers the results are pretty interesting. The pouch weighs in a about 5 grains, I tried to keep the variables as close as possible for comparison's sake...those 2 grains wont effect the velocity to be noticeable at these low speeds. The 9-11 degree change in temp may play a small factor in velocity as well, I don't know how large at this point as I do not have 7.5mm to test it with. But if we allow these factors we can see benefits for tapering.

3/4"X1/4"X4" bands saw an average increase in velocity of about 17%! That was with a 3:1 taper. The 4:1 taper set saw an increase of about 30%! Not bad at all. I have alot of 9.5mm steel lying around, I will try to test all these again today to be more scientific.


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