Before you get too excited, this could be as simple as a different bullet, sabot, or powder charge. Also.. were you swabbing between shots?

What kind of powder charge were you shooting -
What bullet were you shooting -
What sabot were you shooting -
Were you swabbing between shots -
Was it hot outside, and were you letting the barrel cool -

What I would do is get some 250 grain Shockwaves or 250 grain Barnes Expanders. I would load 100 grains of Pyrodex RS and do this all over again. I would swab the barrel between shots, and let it cool at least three to five minutes if it is hot outside (grab the barrel and see how hot to the touch it is)

Shoot three shot groups and examine the group. You can then decide if you want to add more powder or not. Your rifle should take a good strong powder charge and still shoot very well.