I 'tend' to shoot groups at 25... if i can get 5 into the the 10 ring on an NSRA 25 target, then I usually pay more attention to see how tight I can get them with a little concentration, looking for any flyers. If I can't, then I don't usually go further.
Once I have a short list I usually then take them outdoors for 55 yd and see how they perform... with a selection you can usually determine if it's you/gun or the ammo if it's not performing well (or to expectation)
It isn't very scientific, but if i can get a pellet to do what I want it to do consistently then i'm happy.
I normally shoot 5-10 shot groups outdoors. If I see something peculiar, then I might shoot more. But after a certain amount I tend to start a new group as they can often just fly into the hole and tell you nothing new, apart from they're working.
If i'm trying something out, like weighing or sizing, I batch them and shoot them blind... i write A, B , C on bits of paper, and swap those with the spec and then get someone else to keep a record of what they are...