I had a Remington 270 semi auto once. Darned thing would just not stay consistent. My son (who is an excellent shooter) and I took it to the range after a couple of really screwy hunting episodes, and shot it about 20 times to get it where we wanted. That was 2 inches high at 100 yards. We got a 1.6 inch group of 3, which aint great but will do for a deer rifle. We let it cool a few minutes between each shot.
2 days later we went back to the range. The first shot I made was 6 inches high and at least that far to the left. Then my son shot it and was nearly at the same place.
For some reason, that gun woul not hold zero. I traded it for a Winchester model 70 and mounted the same scope with the same rings on that gun. It worked fine.
The effort required to find the problem was more than I was interested in putting out. A different gun that I liked would have been different.