dimples to reduce drag?

[John in WI]

I've been trying my hand at "tumbling" buckshot to make it rounder. I was sloppy about cutting some of the spures and was hoping I could knock some of the flat spots and protrusions back in to round. It wasn't working too well (it's water dropped, lino-enriched WW), but when I started to take the whole container and violently shake it, the balls are starting to change appearance.

Then it dawned on me--if dimples reduce the drag on a golf ball why shouldn't dimples on round balls or even conventional bullets do the same thing? Tunas also have scales that are scooped out a little bit, and there are theories claiming that this reduces water drag and makes them the fastest critter in the sea.

Does anyone know if dimpled boolits has been tried? They wouldn't have to be large dimples like a golf ball I don't think. I've seen a few racing sailboats, and those had a kind of ultra-flat paint (and from I can gather--they NEVER wax them).

[camaro1st]

mythbusters did a show on the dimple theory and used a car for speed and gas mileage. Even with the added weight of like 4in of clay, the dimples won out.

[I'll Make Mine]

I don't know that dimples improve anything at high subsonic to mildly supersonic velocities (especially on buckshot at muzzle velocity of around 1500 ft/s). Dimples work by ensuring that the boundary layer becomes turbulent near the forward end of an object or surface; this prevents a laminar boundary layer from building up excessive thickness, which produces lots of surface drag. The faster you go, however, the less this is needed, because faster flow becomes turbulent on its own in a shorter distance. Once the flow is turbulent, the dimples not only don't help, they increase the amount of turbulence and add vacuum areas that add form drag. Golf balls are dimpled, have been for 80-90 years, and they were pebbled before that for a century or so (same effect, slightly less effective, but easier to mold with 19th century technology) -- but cannonballs have never been dimpled, pebbled, or (after they became elongated, rifled bullets) ringed, and I'd be amazed if someone hadn't tried it at some point after texture was added to golf balls. Supersonic flow is best with smooth surfaces, for certain -- and subsonic flow much faster than a golf ball's flight is too (else airplanes would have been dimpled for the past 30-40 years at least).

[35remington]

Buckshot BC sucks, period. And dimples won't help turn them into a boattailed Berger VLD bullet.

Any improvement, if present, would be impossible to see. As a round ball is second only to a brick in poor aerodynamics.

[Jim]

What's that old adage about "You can paint a pig pink....."?

[Four-Sixty]

If we're talking about improving patterns I'd like to test the idea of keeping the buck from spinning as long as possible.

I've stacked 3X3 00 buck and put a cardboard disc between each layer. In my first two tests it appears the added cardboard discs really tighten the pattern. I can only speculate that this is happening because the balls are "locked" together for a brief period longer than the balls not stacked with cardboard discs.

[plainsman456]

It will help if you have the forcing cone in your shotgun reamed.

[fcvan]

I read on here where a guy was using two round flat plates with one being turned by a drill press. I believe the press was adjusted to lower to a set measurement so that when the round balls were rolled/pressed it removed the imperfection and the rounded out balls would then spin out from under the plates. I would assume there would be some sort of opening to let the finished balls out at a certain spot for collection. Someone else talked about using two hard flat surfaces and rolling them by hand. I have tried neither as I have only used round balls in front loaders and percussion revolvers. I will try the boards first as I don't have a drill press in my shop - yet. Frank

[MtGun44]

The dimples cause the boundary air flow (right at the surface) to transition to turbulent
from laminar flow earlier on a reverse taper. This turbulent flow stays attached to a
reverse taper (back side of a golf ball) a bit longer then laminar flow, so the area of the
separated flow (wake) on the back is smaller, so lower drag.

This is NOT the situation on normal boolits (no spherical rear end) so it is not applicable,
and never applicable to supersonic or near supersonic flows. The wake of a boolit
is defined by the base. At very slow velocities dimples on ONLY the boattail MIGHT
possibly shrink the wake a touch. At high subsonic or supersonic (the only velocities
that we use) no significant effect. So - geometrically inapplicable to the great
majority of designs and velocity inapplicable to essentially all firearms.

If it was going to work anywhere, try a roundball at extremely low velocites, like
500 fps or something. Should make a measurable diff on a BB from an air rifle.

Short answer: It's not going to work.

Bill

[popper]

John - that's called vibe tumbling, used to deburr all kinds of stuff. So if you have a tumbler, dump the shot in and let it run. actually some of the new shot is not round, supposed to cause more bird damage and a better kill.
PS - the dimples @250fps, the 'speed limit' for golf balls, allow backspin on the ball to create lift and give a better trajectory. With no spin, they just restrict the fps.

[Idaho Sharpshooter]

popper, and the group;

several years ago, I tried to patent the dimple for paintballs.
the patent office nixed it, said I could not prove any improvement in the flight characteristics. APB company sent me an Email later, saying they had spent about $100,000 and came to the same conclusion.

[popper]

Agree, you can't put backspin on the paint ball. I almost got put on a project to do very high speed video of golf ball ballistics for pro training. Got pretty good lesson from customer techs. Project was a success, I just got put on a blood cleaning project.

[Bigslug]

No benefit on a rifled projectile, or one that spends most of it's travel time at supersonic speeds.

One of the problems with non-rifled guns is that air can compress on the leading surface and spill off to one side or the other, disturbing the straight-line flight of the bullet. Rifling fights this with the gyroscopic effect, and possibly does something to help the air spill off evenly.

Dimples break up that uneven air spill, allowing golf balls - and theoretically, round, unrifled bullets - to fly straighter. They probably WOULD have tried it on cannonballs if they were still a valid military projectile in the time of the dimpled golf ball. Figure enough generals play golf for the idea to make it over to the artillery side.

But here's the thing - you can have your shotgun's bore modified with a longer forcing cone and back-boring, (such as by Vang Comp) and this will consistently give you nine 00 pellets on a silhouette target at 25 yards all day long - PRETTY MUCH REGARDLESS OF WHO'S AMMO YOU'RE SHOOTING. One moderately expensive barrel mod versus constant fussing over ammo? Easy call to make, IMO.

[35remington]

Or you can do much better than a Vang Comp barrel in tightness of pattern by simply buying Federal's Flite Control buckshot and shooting it through a plain, generic cylinder barrel out of your home defense shotgun.

Cheapest solution of all. Vang Comps, chokes, and other traditional barrel based methods of holding a pattern together don't hold a candle to it.

Four Sixty, stacking carboard disks between layers of shot, or maybe buckshot, is considered to be a "spreader" type load. If you think on it a bit, you can see why this would be so......and it is.

Federal has proven that the way to keep patterns tight is to keep the buckshot in the wad as long as possible, so air resistance has less time to force the shot to spread.

[MikeS]

I really think I once saw a video where the army was doing tests with dimpled bullets. The end of the video was that the army wouldn't say if there was an improvement or not. Typical military hush hush type of answer. But then does any really believe the russian fishing boats that follow each of our submarines around are really fishing? Or that we don't (or didn't) have a similar boat tailing each of their subs? Does anyone not know what we called our boats that did that?

[Cap'n Morgan]

Remember this one?

http://bulletin.accurateshooter.com/2009/04/us-army-team-tests-radical-new-dimpled-bullet/

Notice the date, though...;)

[I'll Make Mine]

Don't forget to read the follow-on article...

http://bulletin.accurateshooter.com/2009/04/dimpled-bullet-spoof-continues-to-fool-web-readers/