Dimpled Ball

[atr]

Somewhere in the 1940s British bombmakers were trying to design a bomb that would skip across water then sink and blow up a dam . One of thier most successfull experiments was with large round containers filled with explosives and they made an amazing discovery while trying to propel spherical shaped bombs . If they dimpled the bomb it would travel twice as far as a smooth surfaced one with a trajectory half as great . They invented the modern golfball . The round ball causes drag behind it slowing it down quickly and shedding energy while a dimpled ball disturbs the air in a totally different way and the resulting drag is half as much . With the same ammount of energy for propulsion a dimpled ball will travel twice as far as a round one and travel in a trajectory half as flat , which brings me to our kind of roundballs . We use minis and maxis for hunting because the round ball , due to it's airodynamics slows down , sheds energy and drops like a rock . It works on bombs and it works on golfballs so why wouldn't it work on our lead balls . In fact in the british experiments they did use marbles and lead ball and the dimpled ones did just as expected . Has anyone ever tried to design a dimpled roundball or a mould for such ? I see no reason that with a tight patch a dimpled roundball couldn't shoot accurately , trajectory and energy comparable to a maxi . The dimples on a golf ball are not deep so with a snug patch i see no reason that there would be a gas blowby . Comments ?

 

[Stumpkiller]

May well work, but a bomb and a golfball both travel relatively slow compared to a bullet. The dimples disrupt the boundry layer on the smooth surface, allowing less friction (air resistance). Americas Cup sailboats and nuclear subs have a slightly rough wetted surface for the same reason.

Now for the hard part: how are you going to dimple the balls? It would be impossible to cut the mold with a round burr. It would have to be swaged with a machined male squeezed under great pressure into a soft mold - maybe aluminum. But, because of the dimples a two-piece mold wouldn't work. The dimples nearest the edges would hold the cast ball. A three piece mold would be pricy and require a more complex clamp than pliers-type handles.

 

[MacTavish]

I have see some of the smoothbore shooters at Freindship and other matches 'dimple' their roundball between a big, course file & the loading bench. They use the same 'discussion' to justify doing so.

 

[roundball]

Actually I think a tumbler might work well...here's why:
I bought 5 boxes of Speer .530's on auction and all the guy did was put the 5 plastic boxes inside a box the size of a shoe box, without any packing material, and shipped them.

All the plastic boxes broke apart, and 500 loose balls rattled and rolled and 'tumbled' about for a few days shipping...they all got very uniformly dented/dimpled all over from banging into each other for days...looked like miniature golf balls.

Took them to the range and they shot just as perfectly as brand new ones.

 

[Randal Zartman]

Would we need to paint these new fangled dimpled round balls orange so that we can use them when there is snow on the ground? :crackup: :crackup:
Zman

 

.............

 

[smoke]

I built a smoothbore in high school 30 years ago and the old geezer who sold me the parts said to dimple the ball using a rasp. Rifled barrels are different though as the ball is meant to spin, dimpling a round ball for in a rifled barrel will probably get you odd shots.

 

[silverfox]

Zman: Paint them ORANGE and watch them go down range in the sun. Strange to see tracers from a muzzleloader.
Fox :thumbsup:

 

[taylorh]

I think your on to something. I mentioned this once before but didn't get a responce. I would be suprised if dimpled balls retained their velocity longer than smooth.
Taylor in Texas

 

[loophole]

The dimples on golf balls work only in a fairly narrow range of projectile size and velocity. I don't understand the physics, but it begins with the fact that the compressiblity of air is constant, so different size objects of exactly the same shape have different effects on the air they travel through. The same factor accounts for the fact that at common ML velocities larger calibre round balls have a better ballistic coefficient (which is a measure of how smoothly the bullet passes thrpough the air) than smaller ones and for the fact that the ballistic coeffecient of a given bullet varies with changes in velocity. At 1500 fps the dimpled golf ball might not travel as far as a smooth one, and dimples on a round bullet might not improve its streamlining at golf ball velocities. If you Google the term "Reynolds number" you'll probably find more info.

 

[chickenlittle]

Dimples create more surface drag. On relatively slow golf ball, the dimples also let the air flow farther around the ball (past the mid-point) before breaking off. This creates a smaller pressure drag behind the ball. This effect is greater than the added surface drag so the dimpled golf ball flies farther.

At some speed, the object is traveling so fast that airflow breaks off at the same point whether it is dimpled or not. At that point, dimples simply give you extra surface drag.

Over the speed of sound, like a roundball shot, things are more complicated but dimples still won't help.

 

[Slamfire]

Dimples create more surface drag. On relatively slow golf ball, the dimples also let the air flow farther around the ball (past the mid-point) before breaking off. This creates a smaller pressure drag behind the ball. This effect is greater than the added surface drag so the dimpled golf ball flies farther.

At some speed, the object is traveling so fast that airflow breaks off at the same point whether it is dimpled or not. At that point, dimples simply give you extra surface drag.

Over the speed of sound, like a roundball shot, things are more complicated but dimples still won't help.

What'd happen if you kept your velocity sub sonic?

 

[chickenlittle]

If you shoot your roundball at about the speed of a golf ball, say 200-250fps, it may go farther if dimpled. But I doubt it would be that interesting.