Congratulations, it sounds like you have a good shooter there.
Depending on the rifle, load, number of rounds fired, and cleaning method you may get varying results.
One of the biggest factors is whether or not you lubricate and the kind of lubrication you use at the end of your cleaning process.
A round fired from a freshly clean barrel that has a film of oil incurs a very different resistance from a barrel that's been fouled with one or 2 shots. The latter situation may also be easier to reproduce consistent results with.
After shooting .573 with the first 3 shots, did you wait a bit and try it again without cleaning, and again, and so on?
I'd also suggest that you not ignore those first few shots. Rather pay close attention to them and keep notes so that you know what cleaning methods work best for you and whether you need to foul your barrel before hunting or competing.
