Shooting an AR from the ground on side poi shift?

[woodspider]

Attended a three day carbine course and had an observation that I'm sure someone here can explain in laymens terms?
When laying on our sides say the left side of a rh shooter our poi would be at the 9 o'clock position left of our intended impact point instead of dead center as it would be if we sat up vertical this became more pronounced with distance . At 100 yards it was very left of center target, this happenned to all shooters today. We all agreed it must have to do with the guns being zeroed vertically then canted 90 degrees left during the side laying exercises. Is this caused by the scope height / center to barrel centerline difference? Someone link me to an explanation I can share with other students at the course.
Thanks for any help!

 

[BOL556]

Re: Shooting an AR from the ground on side poi shift?

Your wind and elevation switch when the above shooting position. Your wind becomes your elevation and your elevation becomes your wind adjustment. There is also some guys that responded to my very same question. Hope this helps

http://www.snipershide.com/forum/ubbthre...253#Post3232253

 

[hlee]

Re: Shooting an AR from the ground on side poi shift?

When you sight in your rifle, the line of sight is canted downward through the axis of the muzzle. In other words, if you draw a straight line from your barrel, the line of sight will intersect it. Gravity pulls the bullet into the path of the line of sight at the sighted-in distance. (the line of sight intersects the bullet flight path twice) Now, if you turn your rifle 90 degrees, the line of sight still intersects the axis of the barrel. However, gravity is now pulling the bullet perpendicular to the plane formed by the line of sight and the barrel axis. This is why scope height and levelness relative to the gun are important for long range shooting. There are many effects that pull the bullet out of the plane formed by the line of sight and the barrel axis. Sights are mounted directly over the barrel so that gravity is not one of them...

 

[ShortRangeSniper]

Re: Shooting an AR from the ground on side poi shift?

A lot depends on what range you zeroed at. If you have a 100 yard zero then your bullet should be moving roughly 2.5 inches. It sounds like you might have zeroed at 200 meters, which would mean you are shooting roughly 5 inches left when you are on your side. 2.5 inches to compensate for the distance your eyes WERE above the barrel when you zeroed, and another 2.5 inches to compensate for bullet drop at 200 meters. Basically you compensated 5 inches in elevation to put the bullet even with your sightline (point of aim). When you lay on your side that five inches becomes deflection (moves to the side). You are likely also firing low.

The above assumes a 200 meter zero.