Thats true, all 22 ammo isnt the same, even the same ammo lot to lot is differant.
But I wouldnt worry about that for a while. Right now get a couple of bricks and start shooting. You'll get to where you can start telling the differance.
Get to where you are nearly cleaning the NRA 50 FT target in the prone position.
Then start buying in the 50 round packs, buy as many differant kinds as you can, when you find one that shoots then grab it up.
Right now, dont worry about it. Just work on you positions. Go to the CMP bookstore web sight and get one of the Small Bore books put out by the Army Marksmanship Unit. They run about $7 and will give you all the info you need.
A person can learn a lot in small bore shooting, and that knowledge will carry over to other disiplians.