It's not necessarily that the ammo isn't as high quality as you thought, but different rifles like different rounds. Most around here will recommend spending a few bucks and trying every brand you can get your hands on, same sort of firing (IE 5 rounds, 5 minutes, 5 rounds), a couple of groups of each type, and finding what your particular rifle likes best.
You might find that it likes the cheaper stuff, and at very least it's a great excuse to spend some time behind the rifle.
Note: I'm not the guru on this by any means, so the 5-minute intervals may be less than optimum..I'm sure someone will chime in and correct me.
-Scott