# ideal band strength to projectile mass ratio?



## teekan42 (Sep 23, 2015)

After digging around for a while and not being able to find a solid answer, I could use some help with some physics. 
What I am after is; What is the relationship between band (or tube) strength, projectile mass, and the actual velocity (energy) of the shot? 
Obviously a denser projectile will move slower, but it also seems that a lighter projectile out of heavier bands also is not as fast. I suspect there is an ideal "sweet spot" of weight to strength ratio, but have done minimal testing and do not currently have the means to effectively do so either. But I expect some of you more seasoned slingers have got this figured out? Any thoughts on the matter are appreciated. =)


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## Viper010 (Apr 21, 2012)

I have been searching for just such a chart when I first got back into slingshots after a twenty year or so hiatus...

Sadly I have come to realize such a chart simply can not be made. There's too many variables at play.

For instance here's a couple of examples of things that ultimately influence ammo speed :

Ambient temperature. Warm rubber contracts faster.

Speed of the draw and holdtime. If you draw your bands out fast and release immediately ammo flies faster than slow draw and/or hold before release.

Rubber thickness. Thinner rubber contracts faster than thick rubber.

Rubber compound. The "recipe" of the rubber also influences it's speed of course, and some compounds may be more sensitive to temperature change or hold time than others....

You see where this is going, right?

I've found it best to choose a certain ammo for a specific purposes (.177 bbs or dried green peas for bug shooting, 12mm lead for rabbit hunting, and so on) than look what others use to propel that stuff and experiment from there.

But you're right, definitely gotta look for that sweet spot. If the bands are too light, you lack power. If they're too heavy you'll suffer from handslap and premature band breakage.

If you're looking to shoot the heavier stuff, the hunting subforum is a good place to start. There's a special thread there dedicated to effective ammo-rubber combos for hunting.


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## wll (Oct 4, 2014)

Viper010 said:


> I have been searching for just such a chart when I first got back into slingshots after a twenty year or so hiatus...
> 
> Sadly I have come to realize such a chart simply can not be made. There's too many variables at play.
> 
> ...


Been testing for 8+ months.... there is no set rules, only perimeters that give you an idea. A test one day may give a variance the next day as temperature has changed, the speed of your draw, the amount of active force you apply to the fork, etc. .... as the poster above said ...way to many variables.

When I first started I read one of the posters who did an extensive test on tube/band size and ammo speed ...... I have my own chronograph and his tests were not even close to the speed i was getting .... I'm talking me getting 50-75fps + faster.

Your very best bet is to get a chronograph and do your testing with the ammo you will use and the elastic you will use .... just about everything else is just numbers on a sheet !

wll


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## SonoftheRepublic (Jul 3, 2011)

Maybe approach a different way.

What ammo (type/size weight) are you most interested in shooting, and what bands or tubes do you want (or can easily get) to use. And then some of us here can make recommendations based on experience.


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## wll (Oct 4, 2014)

SonoftheRepublic said:


> Maybe approach a different way.
> 
> What ammo (type/size weight) are you most interested in shooting, and what bands or tubes do you want (or can easily get) to use. And then some of us here can make recommendations based on experience.


That would probably be the best, executive thinking !

wll


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## teekan42 (Sep 23, 2015)

Thanks guys. That's really what I was expecting. Just too many variables.

Currently, I'm using regular and some 3/8thish sized marbles.

Edit: I'm also working with some red (.22mm) and blue (.18) therabands that are probably too well seasoned for this application. I'm currently just drawing to my cheek, (29in) and using 6" active length. The red bands were really slinging the small marbles, until they failed (abrasion with frame) after probably 50 shots. After which I polished up the frame really smooth and now CAN NOT keep the silly things securely mounted. May end up mounting tabs to simplify things.

I definitely need to get a chrony. I think I'll invest in a "professionally designed" sling and band set up, as I'm struggling with my homemade in regards to band attachment/lifespan, which is obviously not helping me dial in my band set up for my ammo choice.

But I really appreciate the input! I'll get it figured out soon enough =)


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## Btoon84 (Nov 22, 2011)

Teekan, one thing I'll add to matching projectile weight to band strength. You'll notice a lot more band slap on your hands if your ammo is not matched appropriately for your bands. Lighter ammo with heavier bands is notorious for causing bandslapitis.


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## jazz (May 15, 2012)

There can not be objectively identified and defined "sweet spots", as in your question, simply because the critical relations in our sport (basicaly in ballistics) such as velocity as a consequence of the power of the draw (at given stretch ratio, weight of the ammo etc.) are continious variables with no "bumps", inflection points or so which might imply, by some standard, a "special spot" which we could, then, call "sweet spot".

(By the way, if you use more and more powerful draw for a given weight of the ammo and at given elongation and stretch ratio, then the velocity of the ammo will rise, true, but not proportionaly; it will rise less which gives a curve somewhat "tired" look as it grows.

However, the "sweet spots" do exist except that they do not reside in the mathematical relations of various variables per se, but rather those spots - although being based on those mathematical relations - are highly personal and circumstantial.

Since I do not know anything about you, I will take myself as an example: as of few days ago I am 62; I have somewhat scre*ed shoulders and I have problems with my joints in my hands/fingers.

Now, how do I find my ways through the objective, phisical reality of various relations in our sport?

First, it is true that ammo flies faster for a given setup, the smaller it is, like lead ball of 5 mm for example, yes! But - and there is a big BUT there - my fingers can not effectively manipulate 5 mm ball at all; for me it is so unimaginable that I have an impression that if I could do that than I would be able to twist moscito's ball, too.

So, from my experience, my lowest mangeable ammo diameter that I am comfortable with is 9.0 - 9.5 mm (more than that and I again start to be clumsy).

S0, if it is a lead ball of 9.5 mm then, in order to fly fast enough I have to put up a bit stronger setup - and there my joints come in which say: "Yes we can do that, but we are not comfortable with that". However, if it is a steel ball of 9.5 mm, then the thing becomes imediately easier since I need weaker setup and still enjoy decent speed.

Now, you think maybe that I go for 9.5 mm steel, right? Well, no.. there is another variable that I forgot to bring in, and it is the fact that I am stubborn enough to go for a 9.5 mm lead ball, in spite of more strain on my hands, more shaking for that reason, and worse results in target shooting. But, hey, this is my trade off, for good or bad, and it does not have to be somebody else's. Okay, I must admit that I like lead simply for its "ammo immage" but also for the fact that I have a lead mold and I can cast them very cheap, whenever I want. Thus, a new variable sets in . ecocomic one!

It is clear that some other person, with other physical abilities but also with different interest, reasons, views and circumstances, would think completely diferrently and this is why I said that although there is a lot of (very complex) objective math in the base of what we do, the "sweet spots" are very personal, and even changing as the person changes in some relevant sense.

I see that you are thinking about buying a crony, that will help, but I suggest that you also read about ballistics and get a grasp of how a given variable changes as some other variable changes too; then, there is lot of interesting material in our Blog section, but also in Setups section - other peoples experince and wisdom ready to be picked up.

cheers,

jazz


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## teekan42 (Sep 23, 2015)

Cool.
Btoon, I discovered that phenomenon, and changed my rigs to ttf. Haha but I also believe I would have remedied the problem with some new lightweight tapers.

Jazz, thanks! My goals aren't necessarily to find "the BEST setup possible", but rather just gain a better understanding of how these things work. I just don't have enough shots downrange to start dialing my stuff in. 
Thanks again!


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