There’s a dictum in retailing that location is everything; so it may be. But where your groups land on target is also of nut-busting importance. When you go through the agonizing and expensive process of seeing what shoots in your rifle, pay attention not only to group size, but group location on the target.
About the fewest number of shots you can get away with and know anything for real is nine in three, 3-shot groups. This is pretty damned scant, and I prefer four or five groups, and in a rifle that’s for targets or varmints where you shoot lots of rounds at a time, 5-shot groups.
It’s possible to fire three decent groups in a row that are nothing more than luck. If group number one is 3 inches above your point of aim, but group two is a couple of inches off to one side and group three is one inch above the point of aim, you have a problem, regardless of group size. For whatever reason, your slugs are not stabilizing properly and are wandering like diseased sheep.
If you want to sight in 3 inches high at 100 yards, or 2 inches, or whatever makes your liver quiver, your groups should never vary their location. Every round, from first slug to last, should go into the same place on the paper. If this is not happening, sooner or later you’re going to miss, and it will probably be sooner.
If you don’t handload, you’ll have to switch ammunition to something more congenial. If you’re a handloader, change powders; whatever you’re using isn’t working and it isn’t going to work no matter what you do. Don’t shoot a light-barreled rifle until it’s hot. It will start to walk and will keep shifting point of impact until it cools off. If that tube is too hot for you to grab and hold on, it’s too hot to shoot.
Sometimes you just have to sit there until your damned rifle is no longer hot enough to brand heifers. It’s a pain, but there you are.