It's been my observations watching a few hundred folks learning how to shoot service semiauto and bolt actions rifles accurately, they all make the same error from the get-go. And few ever stop doing it. It's called "finger flicking."
As soon as their nervous system senses the trigger sear release the firing pin, they "flick" their trigger finger forward. That makes the rifle's muzzle jump off the place it pointed at when the sear released the firing pin. Depending on how fast, hard and direction of flick, the muzzle axis moves some amount in some direction. I think it's based on ones safety issue from not wanting to put any pressure on the trigger in fear of shooting another round too soon. . .or just not wanting any pressure from the trigger finger on the trigger after they've fired the shot.
Keep the trigger finger back against its stop until the rifle's stopped moving from recoil. Only takes a second. This is called "follow through." Harder trigger pulls require a more firm grip on the rifle's pistol grip to master this simple exercise. But it can be done with even a 4.5-pound M1 or M14 trigger.
Good training tool is to take a handgun with a post front sight with a flat top. Its trigger pull needs to be at least 2 pounds. Put an empty .22 rimfire case atop that front sight, cock the handgun with an empty chamber, then hold it still with the case atop the post front sight. Dry fire the handgun without the case falling off the front sight. To me, it's a waste of time to do any more training until one can do this. . .30 times in a row. Afte they've mastered trigger control, then they can move on to live ammo. If one can't hold the rifle still while the bullet's going down and out the barrel, why do any training with live ammo?
Regarding position, nobody winning matches or setting records has their body and backbone parallel to the rifle barrel in prone. They've all got an angle of 15 to 40 or so degrees depending on what workes best for them.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Last edited by Bart B.; April 10, 2013 at 03:48 PM.