[Bart B.]

OD doctors (ophthalmologist) will tell you that the human eye starts loosing visual acuity (sharpness of vision) after 15 to 20 seconds after one stops breathing; holds their breath, whatever. That happens when eyes are starved of oxygen. So, It makes sense to get one's well aimed shots off when two thing are happening. One's gonna help the eyes.

First, your breathing has to stop. When the lungs expand and contract, they move the body around and nobody holds perfectly still. So take in then exhale a few deep breaths to get the oxygen in your blood up over normal levels. Then hold your breath. This will keep your eyes visual acuity as sharp as a surgeon's scalpel for 15 seconds or so.

Second, although you've stopped breathing, your other muscle that expands and contracts is still moving your body around, but not nearly as much. It's your heartbeat. Don't stop it. You want to see what you do. Heartbeat causes a sort of double figure 8 movement of ones aiming point around the target's center. It's the smallest in prone, a bit larger in kneeling, a lot larger in sitting and the biggest in offhand/standing. If you sling up in prone with a scoped rifle then aim at a target, the movement of the reticule on the target is virtually identical to the waveforms on an EKG machine at the hospital. Shouldering a rifle as it rests atop something on a bench top will help, but if it's held against your shoulder, your heartbeat will still move the aiming point around a little bit.

So, breathe deep a few times, then hold your breath and finally take up the slack in the trigger and squeeze slowly until it goes off. Then hold still until the bullet's left the barrel (this is called "follow through"). If the shot doesn't break within 15 seconds of cutting off your breath, start all over again. Unless it's an emergency then just jerk the trigger back and shoot the darned thing.