Friend of mine has a RRA carry-handle upper and a no-name bbl that shoots ragged hole at 100yds with a hand load.  He wants to move to a flat-top to mount a scope in rings and have a better line-of-sight from an optics point of view.

He's concerned about changing the uppers because he thinks when it goes back together, the harmonics won't be the same and he'll never get the accuracy back.  Is this a plausable concern or should he just buy the flat-top upper and swap it all over without much concern?  He's also toyed with the idea of a free float tube as well...

Thx-
~m38a1

Quoted: He's not changing barrels, just putting a different upper on the lower then maybe putting the accurate, no name, upper back on? If that's the case he should be fine. Removing and putting the upper back on should not affect accuracy.

A bit more clarification....
He's wanting to CHANGE from a carry handle upper to a Flat-Top upper retaining the same bbl, gas tube, handguards and front sight.  

should be no different as long as he knows what he's doing.


you would have to re-zero though