The real question is not what is the best group you have ever shot, but what is the average of the best groups you shoot. What I am getting at is I have shot a near one hole group ONCE at 100 yards. It was a real shock to shoot something like that. But I repeat, I did it ONCE.
Now if you take my average 100 yard group they would vary with the rifle I use and the sighting system I am using. I have a couple real good shooting rifles without a doubt not one one of them is a 1" consistent group. My problem is I always seem to get a flier, and I like to shoot five shot groups when I measure a group. My best group was a three shot group because when I saw it, I knew if I pushed my luck, I'd of thrown one..
