Mechanical Offset is the distance between the bore line of your gun and the eye line of whatever device you use to aim such gun. In most firearms, both lines are immediately on top of each other, but in rifles like the AR and the AK, there is s substantial distance and same goes with guns that may be using optics.
The importance of knowing this is because you there is a proper technique on how to shoot weapons with mechanical offset because if the Point Of Aim (POA) is different that the Point Of Impact (POI) on normal guns, the adding of Mechanical Offset will increased so the shot will end up not where we want it.
Here is s simple but effective graphic showing the principle:
Or you can watch a video with a real life and costly demonstration:
In the next lesson we will be talking about bi-pods, bags, shooting sticks and other devices that can help shooting a long gun without incurring in vehicular bodywork expenses. 😀