19mm band stretch ratio

the optimal stretch ratio is still 3 to 1 , by making the bands longer you are just throwing away power stroke , you would be better off with a thinner band that you can load at optimal stretch.

phil

I believe in Science and empirical evidence. Who has a test fixture set up?

A handy rubber sizing chart from Bluewaterfreedivers in WA

It doesn't have 19mm and is for conventional muzzles, but I think your rubber length would be very tight.
How to use the chart

I can tell you I can't cock bands making 140lb at the wing, but some South Africans can.
Put a scale on that 300% band and tell us what you get with the small id 3/4.
When I have used 3/4 on a 48'' barrel I could only do 250% elongation.

Cheers, Don

Dan, that is the norm 1-3 ((90cm-5cmWisb) / 3 * 2) for all diameter "new bands"

understand that the 16mm more stretched 1-3.5 ((90cm-5cmWisb) / 3.5 * 2)

Dan, esa en la norma 1-3 ((90cm-5cmWisb) / 3 * 2) for all diameter "new bands"

Entiendo que para 16mm es mas corta 1-3.5 ((90cm-5cmWisb) / 3.5 * 2)

Hay información que la banda estirada a mas del 300% afectaba su estructura y en consecuencia la transmisión de energía, esto aplica al latex natural, al polímero o a ambos?.

Ahora,estas usando las tuyas ID de 1mm deben ser mas duras para estirar.
tengo unas black no latex (creo) , son durísimas, rompe pecho, no las quiero, muy duras para cargar y no transmiten la energía de las black/ambar, es mi impresión.

me gustaría probar tus bandas de 1mm.

Ill my measure my 19mm band when I get home tonight

My Father in laws omer came with a 19mm band and we both struggled to load it - changed it over to a 16 now - so much nicer to use but does have slightly less power (not really an issue though).

I have my 90's loop style band cut at about 62 cm. I had an even shorter band on it before but it took an act of God to load it. I wouldn't go any shorter than what I have now and I wouldn't hand it to anybody expecting them to load it. Even with a wet suit with a chest protector I usually end up with cuts and bruises on my chest from loading it for a day. But it hits like a hammer.

Quote from Jono

My Father in laws omer came with a 19mm band and we both struggled to load it - changed it over to a 16 now - so much nicer to use but does have slightly less power (not really an issue though).

Wouldn't two 14s have about the same power?

Batch to batch rubber is going to have variance. No one know more about this than Don.
I just tied up some 5/8" Primeline rubber at 300% elongation on a short gun and I could not load it. Not because I could not pull any harder. But it just felt like it was done stretching. It was pulled as far as it wanted to go. Kind of like using a torque wrench, sometimes the feel of the bolt being stretched gives a better result than a torque wrench. I only needed a 1/4" longer wishbone, but on a short band, a 1/4" is a long ways.

Dusty, good quality rubber such as Dan's can handle 300% elongation, I have not taken it past that as loading becomes a issue for me. I start by first cutting my bands to 250% than I elongate them for 2hr of soakdown.
Before I hunt with the gun I retie the bands at 300% elongation to achieve consistent max power delivery.

I don't know about Dan, but I know of one big manufacture that had rubber that could not be cocked to 300% elongation by most of his customers that weren't Aussie or South African, than the guns went out with 250% percent elongation. Later the rubber was reformulated to have more elasticity and produce less power. Guys hate when they buy a high end gun and can't cock it in front of their mates. A lot of rubber is produced today with this in mind, such as 19mm bands with soft compounds and large ID holes. Euro gun builders tune the band composition and size to produce a powerful but smooth shooting gun.
Us Yanks sometimes keep trying to hang the thickest and shortest bands on every thing we shoot.
My guns have mass designed in to allow me to run at full throttle, that my shooting style and aim has grow accustom to. The Aussies on the West coast have learned in the past 30 years that one thick 19mm band on a long springy 6.75 or 7mil shaft can get the job done too. Two different hunting styles with gear to match,
both kill fish in the right hands.

Cheers, Don

My last order of 3/4 tubing came with a complimentary cycle of roids and a livestrong bracelet....

Quote from Dan

First it's questionable what the gun length measurement actually refers to. And they have it in millimeters? why. In any case if 900 is 90cm, then a 20mm band at 60cm is right where I started (30cm x 2). I have to call BS, there's no way an average person is loading the 90cm stretch speargun I have here with 60cm of 19mm rubber. And then there's the short measurement LOL. Well maybe with a 1' wishbone..

I've made up plenty of rubbers based on that chart and they load fine, but with some brands of rubber it can be a bit short. Did you click the link which gives a bit more info on the gun length measurement?
I never expected to get called out by an American for using funny units! :laughing:

Just for clarification, how are you all calculating % elongation? I get the stretched to relaxed ratio is 3:1, but are you including the relaxed band length in the % elongation? In Dan's example, is it: 30 cm (relaxed) + 60 cm (stretched portion) = (90 cm/30 cm) x 100% = 300% elongation, or is it: 60 cm (stretched portion) / 30 cm (relaxed length) = (60 /30 ) x 100% = 200% elongation? :confused2:

Quote from Dan

Interesting take. But I don't think you'll achieve the same power as this 19mm band at %250, with a 16mm band even at %400, irrespective of the 19mm pulling over a shorter distance. I could be wrong, lets hear more opinions.

A 16 mm band at 400% elongation generates 144 Lb. of force. A 19 mm band at 250% generates 153 lb. of force. The 19 mm band at 250% would generate the same power at 28" as the 16 mm bans at 400% would at 30".

Wood guy, on my guns I take specimen length X 3 .

Round numbers as a example.
Initial length, L0=100mm.
Final length, Lf = 400mm.

Change in length, dL = Lf-L0 = 300 mm

So, percentage elongation = 300*100/100/100 = 300%.
300% means the elongation is 3 times the original length, which is 3*100 mm.

Cheers, Don

I've found that for short range shots, 19/20 mm bands are better (more explosive) than 16 mm, which are better for long range shots because they will push the shaft for a longer period of time. Of course, I use 2 x 16 mm for my long range gun.

Take a look at these charts from an Italian on-line store. Maybe you need to hit the gym...:rolleyes1: