Hmmm, good question. Nowadays my old eyes only let me get 3" groups with any gun over iron sights at 25m, I know my limitations and accept that. I have done 5" with my revolver a few times so for me it has to be the pistol or its load that is not letting me pull it in tighter.
I have seen reports of people shooting clover leafs with them, but till I see it with my own eyes........
Try another gun, perhaps an underlever gallery rifle, with iron sights. Work out how good a shot you are, then compare how you are doing with your revolver.
If you can do 3" with another gun over iron then 3" with your m/l means you have got it right.
“If a cricketer, for instance, suddenly decided to go into a school and batter a lot of people to death with a cricket bat, which he could do very easily, I mean, are you going to ban cricket bats?” :- Prince Philip said after Dunblane