Remember the Stobor

Sometimes I have partially remembered stories that tug at the fringes of my conscious memory.

They smolder away until they pop into focus. Then they show up on the blog.

One of those stories involved somebody in the US shooting community who built very, very expensive long-range target rifles. Long-range meaning 1000 yards.

He used the finest components, the best barrels yada, yada, yada.

One day, he heard about a shooting competition in Britain that was some ludicrous distance like 2400 yards (a mile-and-a-half) and all of the competitors shot the "obsolete" .303 British. He was like a shark smelling blood in the water.

The only requirement, if I recall correctly, was that the rifle had to be have a bore of at least 0.300"

The top cartridge is a loaded .303 British. The middle empty brass is a .300 Winchester Magnum. The bottom is an empty .308 Winchester which virtually duplicates the .303 British ballistics. Empty .308 included in image to minimize optical-illusion effect of loaded round.

Before the competition he made a number of side-bets. One of those side-bets involved his rifle which he valued to be in the neighborhood of $7000. After all, how could a souped-up 300 Winchester Magnum in a Rem 700, aluminum billet-stock and a premium trigger lose to a .303 British SMLE (two-piece wooden stock) at long range? After all, the .303 British was such a slow mover that small plane traffic was diverted away from the competition as the bullets were over 300 feet above the ground at their apogee.

The rifle builder, who was truly a gifted shooter and rifle builder, went back home with a lighter wallet and without his custom-built "British beater". He didn't just lose, he was soundly thrashed by a very large number of shooters.

His after-action-report claimed that the two-piece SMLE stock has some mysterious harmonic that vibrated in a way that brought the bullet back to the target at 2400 yards.

From the engineer's perspective

The "harmonics" argument is pure poppy-cock.

Expecting the "harmonics" of a gun stock flexing after the bullet leaves the barrel to influence the trajectory of the bullet-in-flight is an example of "cartoon physics". That mental model may be intuitively pleasing, but it is wrong. 

So, what really happened?

The major clue is the fact that the .303 British bullet tops out at 300 feet above the ground.

Consider that the trajectory of the .303 British bullet is 30 feet above the ground and rising at 200 yards in order to hit a ground-level target at 2400 yards while the .300 Winchester Magnum's trajectory is much flatter and it spends 400 yards in the highly turbulent and unpredictable boundary layer before punching through the 30 foot ceiling.

Why is 30 feet significant?

Simulation by Jesse Combs, Ph.D. University of Adelaide, AU. The dirty-air created by blunt objects protruding from the ground is only slightly higher than the object itself.

 

 

Because objects on the ground generate turbulence and shed von Kármán vortices. In an urban or rural environment most objects that stick up, out of the ground are roughly 30(ish) feet tall: houses, trees and such. That dirty air imparts a sideways velocity on the bullet that affects the bullet through the remainder of its time-in-flight.

Gravity is not a constant. A gravity anomaly map of Michigan. I live in the Michigan rift.

Unlike wind, gravity is reasonably constant over time and can be dialed into a scope. As long as the initial velocity and ballistic coefficient of your rounds are constant, gravity is a non-issue. 

Wind gusts and variation in wind-speed encountered by the bullet as it travels toward the target are the devil.

And the intermittent, gusting effect smooths out considerably above 30'.

By virtue of the rainbow trajectory mandated by their pedestrian velocity, the .303 British pops above this "dirty air" much sooner than the faster shooting .300 Winchester. Note that this is NOT the case for 1000 yard shooting. In that scenario, the .303 British tops out at about 15' above the line of sight and never leaves the "dirty air" boundary layer.

So why blog about this now?

Things might get bouncy soon. Where we spend the majority of our time will be far more important than the vintage of our "gear". The sooner we depart from the turbulent, dirty-air the better our lives will be.

The US shooter who got spanked by the Brits made the assumption that shooting a mile-and-a-half was incrementally different than shooting a thousand yards. That assumption was fundamentally flawed. Not only had a new variable shown up but it dominated the results of the competition.

And that is why our environment today is so vexing. New variables are showing up but are they "game changers" that change the rules? Perhaps more precisely, WHEN will the rules change? What events will be the signal that we put away the .300 Win Mag and switch to something else? Will it be "The knockout game" coming to your city and the PA not prosecuting and the press not reporting? Will it be structural fires the Fire Department does not respond to?

Events can move very, very fast. Technology will not save you. For my part, I would rather have a single-shot .22, Tee-shirts and good neighbors in rural Eaton Rapids than a machine-gun and body armor in any inner-city in the US. Your mileage will vary.