Re: What causes horizontal and vertical strings
What some folks are saying about vertical shot stringing in this thread is, IMHO, way off base; probably out of the ball park.
Consider the fact that a .308 Win. has a 2/10ths inch vertical shot stringing at 100 yards for a 100 fps spread in muzzle velocity. And a .300 Win. Mag. shooting 180-gr. spitzer boattails out at about 3000 fps with a 100 fps spread in muzzle velocity has vertical shot stringing at 200 yards of about 6/10ths of an inch. If vertical shot stringing is more than this, there's something else causing it. And a rifle capable of 1/8th MOA groups of the shooter at these ranges is needed to see these effects of a 100 fps spread in muzzle velocity.
Most common problem shouldering a rifle as it rests on something atop a bench is where the butt plate's put in the shoulder; too low and shots go high; too high and shots tend to go lower. In second place is how hard one bears down on the rifle's cheek piece with their own head; too hard and shots go low, too soft and shots go high.
Horizontal shot stringing from rifles so shot is common when the rifle's not pulled back into the shoulder the same way for each shot. There's also a shift in windage zero from sitting at a bench to standing up on your hind ligs; shots to to the right more so when at the bench.
If the rifle's trigger has a really heavy pull, the impact of the trigger finger transferred to the rifle when the sear's released and the finger lever comes to a hard stop is quite a force. If that force is not in line with the bore axis, it'll pull/push the rifle to one side. Good way to see this is dry firing and watch were the scope's reticule moves when the firing pin snaps home. If it jumps left for a right handed shooter, the trigger finger's not far enough onto the finger lever; it pulls back at an angle from right to left. If the trigger finger's too far in, it pulls the rifle to the right moving the recitule that way when the firing pin snaps.
One sure way to have horizontal shot stringing is finger flicking when the round fires. That's when the trigger finger's unconciously told to jump off the trigger's finger lever when the sear releases. You gotta keep that finger on the trigger with it at the stops until the rifle stops moving from recoil. Practice doing this so it's second nature. Finger flickers never shoot very accurate. This is called follow through.
Last edited by Bart B; 05-12-2011 at 08:17 PM.