Get that butt tight in your shoulder. If you don't, two things will happen. One: You'll waste a bullet. Two: You'll break your arm.

11 seconds sound clip from the The Magnificent Seven (1960) movie soundboard.

You can hear this line at 00:57:21 in the Blu-ray version of the movie.

Quote context

[...]

- He'd never send men ahead if he was near enough to see for himself.

- So we have time to get ready. And we have something else: surprise.

- If he rides in with no idea of the reception we can prepare for him, I promise you, we'll all teach him something about the price of corn.

- Aim, squeeze, cock. Aim, squeeze, cock.

- Settle down. Now, you miss the first chance, you may not get a second.

- Get that butt tight in your shoulder. If you don't, two things will happen. One: You'll waste a bullet. Two: You'll break your arm.

- Now, close your eye. Aim from here, to here, to the target.

- Fire.

- That rock?

- No, that man you're gonna kill.

- Good!

[...]