new jacket..

[colo native]

Interesting article from The Shooting Wire.

Bumpy Bullets Better?


In golf, dimples are the wings of a golf ball. It's not the high
coefficient of restitution that gives a ball it's distance, although the
compression (that's COR) does help with the slingshotting effect off the
club face.

Nope, it's the dimples and their displacement of air that keeps the ball
tracking further and straighter.

That's why the number and pattern of dimples are a big deal on a golf
ball. Most everything else is marketing, but the dimples really do make
a difference in ball flight characteristics.

Technically speaking, it's the result of relocating air and creating a
turbulent boundary layer that moves the separation area (the area where
the exterior surface of the ball no longer creates friction with the air
molecules) further back on the surface.

The result is a thiner wake, making passage through the air easier.

It's all about being more aerodynamic and less of a drag.

We'd heard the U.S. Army was looking into bullet technology with the
goal of giving snipers a flatter shooting bullet that was more, well,
slippery. Apparently, U.S. Army officials at the Aberdeen Proving Ground
have moved bullet technology forward - using some of the principles used
in golf-ball technology.

Bullets, if you look at them, have not truly been created for optimal
aerodynamic characteristics. The nose of the bullet has changed, but not
a lot has happened beyond the nose.

That's the equivalent of making an aerodynamic bumper, but putting the
same old square truck behind it.

The Army is now testing changes beyond the nose, evaluating a dimpled
bullet that has reportedly reduced projectile drag, yielded a flatter
long-range trajectory with much more retained energy at the target.

Their search for "slippery" may have actually yielded the next big break
in bullets.

After testing circumferential drive bands, dual-radius ogives, and
rebated boat-tails, the dimpled bullet was given a try.

It was the long shot of the group (ouch) - but it absolutely no one
expected the performance it has delivered.

Nominal drag coefficients (Cd) have improved- markedly- and muzzle
velocities have jumped +80fps in .308 test guns.

Terminal performances have been described as "spectacular" giving
snipers a more slippery bullet with enhanced long range performance and
way-better results on "soft targets".

In short, the Army's already a potent snipers have been given a
better-killing bullet. So much better that some of the dimples in the
ongoing tests have come from the smiles on the faces of the testers.

The design for the new dimpled round is reportedly a copper-jacketed
bullet with dimples about 0.5mm in diameter. Early tester rounds were
produced in binary impact swages that press-formed the dimples after the
bullets came from conventional dies.

Next-gen bullets will be made using an advanced metal-injection-molding
(MIM) process, putting the dimples directly on the surface of the
bullet's jacket. That new high-tech jacket is being called a MIM
Exo-Jacket (as in exoskeleton).

The core's composition remains classified.

With lowered drag the dimpled bullets exit barrels faster (due to
reduced surface friction). And while the .308's +80fps in added
performance is exciting, the higher-pressured .338 is picking up nearly
150fps. That's somewhere impressive and rapidly-approaching awesome. And
it's with identical powder charges and cases-the only changes were the
dimpled bullets themselves.

And then there's the unexpected bonus.

While full-metal-jacketed bullets break along the cannelure - that band
around the cylindrical part of the bullet and fragment, the thinner and
more irregular walls of the dimpled bullet have multiple fragmentation
points.

Instead of breaking up, the bullet effectively blows up in soft targets.
Longer distances, flatter trajectories, increased velocities, and
enhanced performance on "soft targets" - sounds like a winner to me.

I always knew whacking hundreds of thousands of golf balls would
eventually do me some good. Just never thought they'd be the basis for
understanding how engineers were improving bullet performance.

[Rusty]

I wonder how that would work with a .338 Lapua?

[colo native]

Have aw look

http://accurateshooter.wordpress.com/20 ... ed-bullet/

[Rimfire McNutjob]

I have a hard time believing that dimples on a golf ball would have anywhere near the same effect on a bullet on the other side of the sound barrier. The fact that the article was posted on April 1st, 2009 isn't helping either.

[colo native]

http://accurateshooter.wordpress.com/20 ... b-readers/

[JReed]

You got me.