Mike15 break-in

Will be putting together my 1st AR build soon with the Mike-15 12.5” upper & folding brace. Reading through the manual it says to run through 400 rounds break in.

How do I tell when it’s broken in? Better groupings? I recall a review saying it was ~200 rounds for their break in.

Any NOOB AR tips for me?

Initially I’ll toss some BUIS and a basic red dot on there & head out to an outdoor range.

TIA!