​How Marine snipers are trained

QUANTICO, Virginia - The success of the film "American Sniper" - the story of how Chris Kyle became the deadliest sniper in U.S. military history - has put Kyle's trade into focus.

We went to the scout sniper school at Quantico, Virginia to see how Marines are trained to become deadly weapons. As it turns out, pulling the trigger is only a part of the equation. A sniper's stalking skills are every bit as important as marksmanship, according to Brigadier General Austin Renforth.

He says the snipers must be able to infiltrate through "an unimaginable distance," - going undetected for miles.

"We've had guys that I know, it's been a two day movement for them to get to where their firing position was," said Renforth.

His only complaint about the movie "American Sniper" is that it left out the stalking.

"They just showed him magically appearing at firing positions and most of the work is done getting you there and getting you out," said Renforth.

Another thing the movie didn't show you is that it takes Marines like Sergeant Ryan Geringer two or three days to assemble a single sniper rifle by hand.

Sergeant Ryan Geringer assembles a sniper rifle CBS News

It is test fired from a stand. At 300 yards the rifle has to fire a grouping of shots no more than three inches apart. At 1,000 yards that translates to the width of a man's chest, enough to cover the kill zone, according to Geringer.

Out on the range we watched snipers hit targets out to 760 yards. They've all been in combat and none of them will talk about it. I asked Gunnery Sergeant Gerald Gavin if he could tell me how many kills he has but he declined to answer.

"It's just not something that we share, sir," Gavin told me.

During one exercise we witnessed, Gavin was trying to find two snipers - Sergeants Scott Haynes and Jared Chambers - before they find him.

In this image is a Marine sniper. Can you spot him? CBS News

"Once we do see the objective we're going to determine where we're going to set in to take a shot," said Gavin.

The snipers Gavin was assigned to spot wore handmade works of camouflage known as "gillie suits." Once they leave the cover of the tree line they switch to what they call "skull dragging," a technique where one keeps his head to the ground while inching forward. Then they set up to take their shot. To outside observers, there's no sign of anything.

Sergeant Jared Chambers in his gillie suit during sniper training CBS News

A successful sniper shot on the battlefield does more than just kill an enemy fighter.

"When you have no idea where the shot came from and then you see somebody around you just drop, that'll send a message at somebody pretty fast," said Renforth.

As for those two snipers we were trying to spot, a marine waving a white stick pointed them to out - but we still couldn't see them.