Monday, February 27, 2012

Range Day Lessons

by Ben Small

It's a good thing my neighbors can't see what I took out of my trunk today. An M4, a M1A, a Glock 34 and an XDm. For those who don't know, the first two are battle rifles, the latter two semi-auto pistols. Two of the above hold thirty rounds or more, one twenty rounds, one sixteen. I'll let you figure out which is which.

Guess you can tell: I spent the day at the range.

There's a certain exhilaration from firing a firearm, a release of tension and a dose of either immediate satisfaction or disappointment.

Sorta like a modern era third date.

And it's tiring. I've been haggard all evening, exhausted, de-hydrated and spent.

Sorta like the morning after that modern era third date.

But there are always lessons learned from a day at the range. And today was no exception. Just observe; you'd be crazy not to look around. People are firing live ammo, you know.

I noticed two things today that at first glance might appear to be unrelated. Not so. Indeed, they represent illustrations of something that writers about shooting should understand.

Let me tell you what I saw.

First, I saw an eight year old girl shooting a .22 rifle from a rest, her barrel supported on a sandbag, the butt end on her shoulder. Her target stood ten yards away, with holes all across its four foot span. The rifle, an old Winchester, a lever gun, its wood stock chipped and gouged, the bluing of its barrel only partially remaining. No rust, no butt-pad. The girl's parents stood behind her, marveling at the way she worked the smooth action, laughing when she said she aimed at the target's armpit. Occasionally, one of the parents would shoot another, more powerful rifle at the table next to her. Their guns were newer, but their setup was the same, barrel on a sandbag, butt on the shoulder. Their targets stood at fifty yards, but their aim wasn't much better than their daughter's.

At another table, a man struggled with accuracy from a brand new rifle. His fifty yard shots spaced too all over his target, the rounds key-holing. I knew his rifle; I own one similar. I knew the ammo he used.

Why couldn't these folks hit where they aimed?

Simply put, it was harmonics, torsional vibration that they'd screwed up. Their stuff wasn't working well together.

As I learned from years of working with engineers who designed complex equipment incorporated into sophisticated systems worked into products which accomplish complicated tasks, everything vibrates, even stationary objects. We just don't always recognize vibration because we can't always see it; we can't always feel it. But when the separate vibrations of components combine into a whole, the vibration of that whole is called "torsional vibration." And when that torsional vibration goes out of tune, things go wrong.

Think of the weird shaking of your car when you hit a certain speed. Go slower or faster and the vibration disappears. Sometimes that vibration can be severe. Indeed, such out of tune vibration can tear some of the components apart. In vibration terms, the out-of-tune harmonics are called "criticals." A critical occurs when something vibrates at its own frequency instead of in a harmonized blend. It shakes, rattles and rolls.

Bored yet? I'm getting to the point.

Let me tell you what each of these people did wrong.

The girl and her parents: They rested the barrel instead of the stock on sandbags. While their rifles were cared for, in no worse condition than most, her parents didn't realize that by resting a barrel on anything, they ruined the barrel's float, throwing off the rifle's harmonics and causing it to fire differently with each shot. A rifle is designed to minimize any direct link interference between the bolt, action and barrel. It's designed to spiral a balanced round straight through a perfectly round tube and out toward a target, all at thousands of feet per second.

Like how Peyton Manning fires a perfect pass to a receiver, scaled differently of course. Ever see a wobbly throw? It's hard to toss a perfect pass when one's arm is smacked during the throw. Same principle for this girl and her parents, their rifles (throwing arms in this analogy) operating at much higher pressures and speeds than any linebacker nailing poor Peyton.

And same result: no accuracy.

The other guy: Wrong bullet weight for his rifling. That's why he had no accuracy, why his target looked as if someone had thrown keys through it.

You see, the guy fired a weapon with 1:9 rifling, and the spiral couldn't stabilize the heavy bullet he used. To spiral, a heavy bullet needs a fast spin. Otherwise it wobbles -- "tumbles" in rifle parlance. And tumbling causes key-holing in targets.

Again, think of a football: the heavier the football, the more spin required to make it spiral.

A 1:9 rifling means a bullet makes one turn in nine inches. A 1:7 rifling means one turn in seven inches. So a  1:7 rifling means a faster spin.

This guy would have been better served with a lighter bullet weight. The rifle functioned properly; he just didn't mate it with the right bullet. The torsionals were off.

Of course, I could have butted in and said something to the girl, her parents and the other guy, but, well...we all know people who do that sort of thing...butt in, that is. One can usually tell when someone wants help. They say something; they scratch their heads, or they stare at you with that lost look. I got none of that. Despite no accuracy, these people were having fun.

Well, okay, I lie...maybe just a bit. During a break, the guy came over and remarked about my tight target groups. As often happens during range-break chats, we discussed our rifles. When I told him I owned a rifle similar to his, he asked what ammo it ate.

Wham, bam! I threw a perfect spiral right through his open ear hole.

Just like Peyton Manning.

And, well...I learned something, too. I learned that if I don't clean my XDm once in a while, it occasionally may not fire.

Some people are just idiots.

1 comment:

Jaden Terrell said...

Ben, I love your articles on firearms. I always learn something new and come away with a story idea or two as well. Thank you!