# 300 fps with a 31" draw?



## M.J

I'm looking for a band setup that will provide a consistent 300+fps with my normal 31" draw length and 3/8" steel. Getting 300+ with a starship is no big deal but I'm after being able to shoot in my normal style. The bands don't have to last forever, obviously. These won't be my everyday setup, just something to shoot at really long distances.
I have Theraband Black and .030 latex for materials. Who has gotten these kinds of results and wants to share?


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## FWV2

Hey MJ! I got pretty consistent readings of 296 to 308 on crony app! with a tripple tapered band setup of the green golds gym band material? the taper was cut from 1" to 5/8" x 11" for a 32" draw! shooting 36 cal lead.

I would think you should get that or better with tapered triple bands of TBB.

Hope this helps some what?

Fwv2


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## mr. green

Thank you, FWV2. Very interesting, I've been tracking this thread. Also thank you, M_J, for posting this question.


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## Flatband

Hi Mike,

I misplaced all my band cut notes but I think a two layer cut of Black Theraband 1 5/8" x 7/8" x 6 3/4" " should move those 7/16" close to the 300 mark. I know what you're thinking too-THE GONG SHOT!!!!!!!!!! :king:


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## M.J

Flatband said:


> Hi Mike,
> I misplaced all my band cut notes but I think a two layer cut of Black Theraband 1 5/8" x 7/8" x 6 3/4" " should move those 7/16" close to the 300 mark. I know what you're thinking too-THE GONG SHOT!!!!!!!!!! :king:


You know it, bud!
Doubled 1 5/8 x 7/8 is a ton of rubber! I'll give it a shot :thumbsup:


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## bullseyeben!

Before I had a chrony I used too try to shoot through corrigated fence pannels with 9.5mm steel, being a few years back I cant be exact but I had good results with a folded fork/band attachment 2 layers cut aprox 50x20 mm pouch @ tied length aprox 170mm.. that could be converted into 4 layers but given a short band life its easier to fold 2 layers. .


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## boby

Here are some calculations for untapered 0.030 inch latex (from Hygenic), 31" draw, a 0.375" stainless steel ball, a 2 gram pouch, a temperature of 22 degrees C, and an effective band length of 5.93 inches (corresponding to the optimum stretch factor of 5.23 for force energy storage efficiency):

Total width per side =1.5 inches: 300 ft/sec, pull = 19.6 pounds.

Total width per side = 1.875 inches: 323 ft/sec, pull = 24.4 pounds.

You can split the width up however you like; e.g., for 1.5", 2 bands per side of 0.75" each. Hope your pouch survives!


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## M.J

Trying for maximum speed with untapered bands seems like an exercise in self flagellation. I'll go ahead and taper them and skip the 20lb pull.


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## Flatband

FLAGELLATION??? I almost got a hernia saying that one Bud! GO MIKEY!!!! :king:


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## pop shot

I'd be surprised if 1.5" of tbg on each side at 6" pull would do it with 3/8" steel. i dont think it would. i think around 25mm to 12.5mm tapered double tbg over 7" total cut would be your best bet with 7/16 to carry some energy. maybe even 20-10 doubles.


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## boby

M.J said:


> Trying for maximum speed with untapered bands seems like an exercise in self flagellation. I'll go ahead and taper them and skip the 20lb pull.


M.J
View attachment tapered31.pdf


You have goaded me into working out speed calculations for tapered flat bands. As with my more recent calculations for pseudo-tapered bands, I use the actual measured force vs pull distance data, and not an ideal spring approach. Such data is taken for an untapered band, and is then used to derive the force vs pull distance curve for a tapered band. In the attached file I show results of these calculations for forces covering the 10 to 20 lb draw range. Looks like you are going to need 19.5 or 20 lbs of draw to get your 300 ft/s. The best tapered result near 300 ft/s is only 9 ft/s faster than untapered, but the tapering could save you a pound or two in draw force for the same speed. See the table in the attached file to see the band parameters (taper, widths, length, etc.) for getting your 300 ft/s.

I know there is skepticism about speed calculations, but can you imagine trying to experimentally determine the best band setup for a given pull force and draw when you need to vary taper, widths, and length of the bands? There is enough reality in these calculations to expect at least a correct qualitative picture of the best range of tapering, widths, and length.


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## Northerner

Thanks Bob! I just finished some quick testing to see what I could get with .030" Hygenic flats (single, non-folded). I tried 1" straight cut, 7" length, 3/8" steel and a 32" draw. The velocity was 222 fps. Next I trimmed the same bands to 1" x 3/4" and set them to 7" length. Velocity was the same 220-223 fps.

My results seem to be close to the chart. The chart shows 220 fps for 1.0" x 0.8" X 7" cut (0.8" taper). It looks like I have to shorten to around 5.75" to 6.0" for 250fps. Draw weight would go from 10 lbs to 13 lb. That's about all the weight I want to draw.


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## Northerner

Bummer! I shortened the 1" x 3/4" bands to 6" length but velocity only increased to 231 fps with 3/8" steel at 32". I was hoping for 250-252 fps, as per the chart. I went back to 7" and velocity returned to 221 fps. I figure that the extra 10 fps was not worth the added stress on the bands and the increased draw weight.

I'm still hoping to read about someone getting 300 fps with 3/8" steel with a 31"-32" draw length and less than a 20 lb draw weight. Heck, I'm still working towards 250-260 fps with a 32" draw and a stagnant anchor.

Cheers,

Northerner


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## boby

Northerner said:


> Bummer! I shortened the 1" x 3/4" bands to 6" length but velocity only increased to 231 fps with 3/8" steel at 32". I was hoping for 250-252 fps, as per the chart. I went back to 7" and velocity returned to 221 fps. I figure that the extra 10 fps was not worth the added stress on the bands and the increased draw weight.
> 
> I'm still hoping to read about someone getting 300 fps with 3/8" steel with a 31"-32" draw length and less than a 20 lb draw weight. Heck, I'm still working towards 250-260 fps with a 32" draw and a stagnant anchor.
> 
> Cheers,
> 
> Northerner


Hmmm...

Let me summarize your results and add a calculated number as well:

Bands unstretched length measured speed calculated speed

1"x0.75" 7" 220-223 221 ft/s

1"x1" 7" 222 230

1"x0.75" (=new) 6" 231 246

For the calculated number I guessed that your Canadian temperature was 15C, which then matches your measured speed in the 1st row. There are then obvious discrepancies in the last 2 rows between measured and calculated. But there also seems to be a discrepancy in your measured speeds between the 1st and 2nd rows, which you have as being equal, yet one expects a 1"x1" (x7") band to be noticeably faster than a 1"x0.75" (x7") band. So some, but not all, it seems, of the big discrepancy in the 3rd row between measured and calculated may be due to whatever caused your discrepancy in measured speeds between the 1st & 2nd rows.

One thing that sometimes happens is that bands can rapidly lose their stiffness. There are two situations when this can happen quickly: 1) The first few times virgin bands are stretched (they also elongate-- remeasure your lengths??). 2) When stretched to very large stretch factors (at least 5.5, or more likely greater than 6.0 for sheet latex). So perhaps the bands have degraded in stiffness (which could be checked by (re)measuring draw force if you had a force meter).

Anyway, it seems there remains mystery.


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## Northerner

Hi Bob,

I started the first set of tests with 1" straight cut. Then I tapered the same bands to 3/4" at one end. Just for fun I just did the tests over again. Results below.

The bands were cut from a sheet that I bought from Tex. They are 10 1/2" long. The taper goes from 1" to 3/4" over the 10 1/2" length. I used the same bands for the 6" test and the 7" test. All I did was slip another inch under the ties at the fork. The fork measurement was actually a hair over 15/16". Right in front of the pouch it is a hair over 3/4". I measured the bands before and after the testing and the measurments were the same. Room temperature in my basement testing area was 18-19C.

*3/8" steel, 32" draw length *

1" x 3/4" x 7" = 221 fps

1" x 3/4" x 6" = 236 fps

The 7" bands are definitely easier to draw than the 6". I pulled the 6" bands at a slightly slower rate to ensure that I reached full draw. This may account for a loss of a couple fps but maybe not. It is possible that I was overdrawing the 7" bands but I doubt it would be much more than 1/4" or 3/8". I did my best to maintain the same draw length and I did reach my anchor for each shot. I think I'm still coming up a wee bit short on the 6" bands. These bands were new when I started the first testing so they have less than 150 shots on them. Maybe a fresh set would give a bit more velocity. I'll have to check the chart again.

Cheers,

Northerner


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## boby

Northerner said:


> Hi Bob,
> 
> I started the first set of tests with 1" straight cut. Then I tapered the same bands to 3/4" at one end. Just for fun I just did the tests over again. Results below.
> 
> The bands were cut from a sheet that I bought from Tex. They are 10 1/2" long. The taper goes from 1" to 3/4" over the 10 1/2" length. I used the same bands for the 6" test and the 7" test. All I did was slip another inch under the ties at the fork. The fork measurement was actually a hair over 15/16". Right in front of the pouch it is a hair over 3/4". I measured the bands before and after the testing and the measurments were the same. Room temperature in my basement testing area was 18-19C.
> 
> *3/8" steel, 32" draw length *
> 
> 1" x 3/4" x 7" = 221 fps
> 
> 1" x 3/4" x 6" = 236 fps
> 
> The 7" bands are definitely easier to draw than the 6". I pulled the 6" bands at a slightly slower rate to ensure that I reached full draw. This may account for a loss of a couple fps but maybe not. It is possible that I was overdrawing the 7" bands but I doubt it would be much more than 1/4" or 3/8". I did my best to maintain the same draw length and I did reach my anchor for each shot. I think I'm still coming up a wee bit short on the 6" bands. These bands were new when I started the first testing so they have less than 150 shots on them. Maybe a fresh set would give a bit more velocity. I'll have to check the chart again.
> 
> Cheers,
> 
> Northerner


Hi Northerner,

Ignoring the "bit over" bit, your tapers, from your description, physically vary from 15/16" at the fork to 3/4" at the pouch, and are either 6 or 7 inches long. The speed calculations at 18C then give 219 ft/s at 7" and 243 ft/s at 6". If the 6" were actually 6.25", then the speed would be calculated as 236 ft/s, which is right on. Maybe we're getting close enough??

One other thing, the speed calculations correspond to about a 1 second hold at full draw; a 5 second hold would reduce the force by about 7% and the speed by about 3.5% (this data based on tubes).

regards,

bob


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## boby

Hi Northerner,

I'm responding to your request (by personal contact) for more speed calcs, but I wanted the calcs to be more broadly available to the other forum readers, hence I'm responding here. I'd also like to add, for others' benefits, that following more conversations between us, we now seem to be in decent agreement between your measurements and the calculations-- the resolution coming from your additional speed measurements and the realization that holding at full draw reduces forces and speeds (e.g., 3.5% speed reduction for 5 sec hold compared to 1 sec hold). Correct me if this could be said better.

Anyway, I hope you find these attached results useful.

regards,

bob


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## Northerner

Hi Bob,

I'm glad we figured out why there were small differences between my actual tests and the chart calculations. The heavier draw weight took me a bit more effort and required a longer pause when reaching anchor to ensure a full length draw. This increased hold time seems to reduce velocity a bit.

These charts are intersting to study. Thanks for posting! This is definitely something worth saving.

Thanks again,

Northerner


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## Arturito

I would like to see a crony result of 300+FPS with a 32" draw, my best audio crony (10m average speed) are 320FPS with a 10mm steel at 20° single TBG 52" draw ... I doubt 300+FPS could be achieved in normal conditions at 32" draw unless a huge pull (and big recoil) sacrificing accuracy ...

Cheers

Arturo


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