Let's get real here. At one time, during the reign of the likes of Phil Sharpe and Col. Townsend Whelen, ten shot groups were the standard for testing a rifle. Then, it became five shot groups and now three has become the norm.
Ten shots is not realistic, nor are five shots, at least with the average hunting rifle.
I have a friend who is a dedicated target shooter, even to the point of competing at camp Perry. He insists that only ten shot groups can tell you what a rifle is capable of producing. He rails at me constantly when I do three shot groups with say my .308 Win.
My testing is more geared to hunting that outright target shooting, so I load up three rounds, take aim, shoot, reload shoot, and reload and shoot again. Not one to five minute wait between shots for the barrel to cool. After all, no deer will wait around while you wait for your barrel to cool down.
Any groups under 1.25" is good enough.
Almost all my rifles will beat that standard.
Of course, your gun rag "egg-spurts" will wait as they have to make the guns and bullets look good.
Now my varmint rifles are expected to give a higher standard of accuracy. They must shoot ten shots under a dime in good conditions. They do.
For cast bullet shooting, things get interesting. The first five shots are usually under an inch when I have a good day. But I usually am shooting 50 shot groups with cast bullets. Now these are bullets that are carefully cast, weighed, gas checked, very carefully lubed and sized, powder charges weighed, brass also weighed, basically verything possible to insure as much uniformity as possible. Shots are space one minute apart in the winter and two minutes apart in the spring and fall and three minutes apart in the summer to insure that the barrel heat doesn't get out of hand. Rifle is a heavy barrel .308 Savage 110. Even with taking the time to regulate barrel heat, it's quite interesting to see the group gradually open up to about three and a half inches by the time you're done shooting that string. It makes no difference whether I clean after every ten shots or dry brush after every ten shots or just don't bother cleaning, the results are, for all practical purposes the same. My target shooting friend also likes to shoot cast bullets and I've gotten him into competing against me shooting the 50 shot group. He beats me most of the time, but usually there's less than a quarter inch difference in the groups. My rifle is an off the shelf Savage 110 silhouette rifle and his is a custom match grade Remington 700 with Canjar single set trigger. Kind of like me running a Volkswagon Beetle against the cars used in the Indy 500.
Still, every man should be allowed to scratch his fleas in the manner which serves him best. Elmer keith said that. So if a three shot group does it for you, great. Five shots? OK. Ten shots? Why not, if it makes you happy. I only stated what works for me and why. Your results may vary.
Paul B.