Ron I wouldn't argue with the groups from either the Parker 275s or the 300 XTPs. Both bullets shot great. What does concern me though is the inside of the bore. Those rough spots almost look like a flaw in the metal and not corrosion. It looks like it got worse after the JB scrub like you opened up something in the metal.
This can occur during the forging process (flakes) because of improper cooling. I say this because the rest of the bore looks pristine.
It would be interesting to see what T/C would say about this.