Ramp rats are the bane of any traveling sportsman. They are prone to throw; bags, gun cases and rod cases as if trying out for a new Olympic event. Now in particular, gun cases with scope mounted firearms inside seem to take the brunt of the punishment. From point A, home, to point B, hunting camp, and the firearm inside has been bashed, dropped, put into a low or non pressurized cargo hold and then bashed and dropped again. No wonder when you get to camp your rifle is way off when you sight in. Outside of the physical punishment, the lack of pressurization in the cargo hold has caused the gasses in the sealed environment of the scope to expand thereby throwing off your zero point. Now the following technique will get you back on paper and zeroed super fast. After you have zeroed in your rifle at home and it is shooting consistent groups, take an old bore sight with the grid pattern and put it into your rifle barrel. Look through your scope and note where the crosshairs of your scope fall on the grid.
My .308 falls one up and one right for center. I note this on the sling of my rifle so I don't forget. When I get to camp and am preparing to sight in, I take out my bore sight. Stick it into the barrel and adjust the center to be one up and one right. Now I can start the process of sighting in and it doesn't take long to punch a tight group. You can purchase a bore sight in the Hunting Dept of Bass Pro Shops Nashville.