In that we have a need to zero a rifle before a hunting trip; I have found this method to provide a free ‘take-a-way’ from that range time and something that could potentially re-establish confidence, should you have a scope or mount problem. Admittedly, I have never actually needed it, but having it available as a reference for elevations as well as a simple way back to your original zero, is comforting. If you have an issue with a riflescope, whether a mounting or the need to change the scope out for some reason, it has the potential to create great doubt concerning your rifle, which is not helpful. Having confidence in your equipment, gives you a mental freedom. While this seems almost too basic to mention you should always check stock screws, but do not over tighten. A physician acquaintance just returned from British Columbia, when he finally got his shot at a Mountain Goat Billy on his last hour, last day opportunity, after five misses under 200 yards, his rifle literally fell out of the stock. This was of course entirely preventable and needless to say he was sorely disappointed.
I will assume that we will limit this to 300 yards, which is much farther than 99% of our shots will be taken.
For this purpose we will assume a zero of +1.0 at 100 yards. First we will establish a group with the center of five shots 1.0” above point of aim at 100 yards. Then we will move (the same target) out to 200 yards then on to 300 yards again firing a group at each distance using the same aiming point that we used at 100 yards, and will use for all shooting. What you are looking for here is an accurate elevation that your specific rifle, scope, and load combination delivers at each distance in your rifle. You will have to use your judgment on windage and not overreact to conditions at the longer ranges for our purposes. If your group is centered at 100 it is likely good at 200 and 300 in calm conditions. There is a joke among competitive long-range shooters that this rifle holds elevation great but the windage is very unpredictable.
Once this is accomplished you should move the target to 25 yards and shoot a five shot group on the same target, using the same aiming point that you used for all other shooting. This will give you a close range reference for your longer range elevations. I like to use a heavy paper taped to the bottom of a bull’s-eye target for this so that the holes and groups are clean. The grid type targets do not have enough definition for me at the longer ranges. I had given away all of the examples that I had so I scrambled to put one together to illustrate. I took a .243 bolt rifle with a box of factory ammo, (something common) and off to the range. Shooting was done with an almost constant left to right cross wind and these are the results. You will most likely not have perfect conditions in the field if you need to do this either. I did this shooting off a rolled up jacket to duplicate some of the conditions that you might encounter on a hunt. Your shooting bench could be a vehicle hood, prone on a jacket, or shooting sticks. So then your process will be to simply tack up or tape this target to a box or some larger backing at 25 yards, and move your shots into this previously fired 25 yard group. Sure, you could just take a picture of your target on your phone and carry along but the phone is just not a practical target!! When you have this available and use it should you have an issue, it will show your guide or PH a level of preparation and knowledge. I assure you that this will give them a confidence in you also, and that is another critical piece of your overall success!
Best of luck!