* Illustration: Christian Montenegro * A steady wind blows across the edge of the cliff, but I ignore it. For the average sniper, the breeze might be a variable that matters. But not for me. I'm lying flat on a cactus-spiked ridge above the desert north of Phoenix, clutching a Barrett M107 long range sniper rifle. It's a semiautomatic cannon that spits Macanudo-sized .50-caliber rounds at 2,850 feet per second with enough force to punch through an engine block or decapitate a man from more than a mile out. But the gun's real selling point is physics. Its big kaboom largely obviates the need for DOPE, data on personal equipment. Putting a bullet into a target takes more than lining up crosshairs — complex equations combine muzzle velocity, ammunition weight, and ballistic coefficient with environmental factors like wind speed and air temperature. But the M107 is so powerful, all I have to worry about is gravity and not flinching when I pull the trigger.

William Graves, owner of GPS Defense Sniper School, teaches Army Airborne soldiers how to use this 5-foot-long gun. He has invited me to this sunbaked backcountry to experience it myself. I'm wearing two types of ear protection — earplugs and an electronic decibel-filtering headset — because the M107's report can be deafening. At a safety briefing earlier this morning, Graves was disturbingly tactical: "Hold the gun tightly when you fire or it will kick and break your nose. If anything happens, take as many gauze rolls as you can and stuff them directly into the wound. If it's something to do with high-caliber rifles, it's going to be catastrophic."

I shiver as Graves scans the terrain and points to a speck on a hillside 700 yards across the canyon. Through the crosshairs of my 14X Leupold Mark 4 scope, it resolves as a head-sized rock. I wedge the stock into my shoulder and hug it tight.

Then a little math. Bullets don't fly forever — they fall in a shallow parabolic curve. Using a ballistic chart that Graves pulled off the Internet, we twist the elevation knob to lower the scope 14 minutes of angle (1 MOA equals 1 inch per 100 yards). I'm now aiming about 8 feet above the target. Hitting the rock should be simple. Advises Graves: "Move the trigger without moving the rifle."

I disengage the safety, wink into the scope, and feel the sting of cold metal against my cheek. I twitch my finger.

Blam! Air punches me in the face, and the recoil shoves me backward. My ears are ringing. In the distance, I see a puff of dust between cactuses. I have flinched. Actually, cowered would be a better description.

It happens again and again. To scrub and soil, I am deadly. To the rock, I am no threat. Graves tells me I'm tensing up, shaking the rifle ever so slightly in the split second before I fire. The trick? Graves teaches me the "surprise break" firing technique. If you pull the trigger slowly you never know when it will engage — so you can't freak out.

My next shots go wide, 2 feet to the left. Graves shifts the horizontal windage knob a few clicks right to align the scope and steps back. "Fire when ready."

I draw in the trigger languidly, making small talk with myself as seconds tick past. One ... If this were a real insurgent, he'd certainly be gone by now. Two ... And if he were hungry, like me, he'd head to the McDonald's 6 miles up the high — POW!

No dirt splash. Nothing moves.

"What happened?" I ask.

"That's what happens when you hit something," Graves says.

I peer through the scope. The rock is gone.

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