I have a few questions about a rifle I am about to take in trade. The rifle has a RRA lower with a Bushmaster A2 upper, 20-inch A2 profile chrome lined barrel 1/7 twist with a KKF fake muzzle brake.
1. I'd like to change out the A2 upper for a Bushmaster flat top with a Bushmaster carry handle- will there be any problems with sight alignment?
2. I usually shoot 55 grain ammo with a 1/9 barrel, will I have any problems with the different barrel twist rate?
Thanks in advance for any help ya’ll can provide.

1)  There should be no issues with sight alignment

2) I've read about 1 in 7 twist barrels spinning the bullet to fast causing it to key hole, but I've never tried it myself.

It will work fine.
Good shootin, Jack

Thanks for the info guys, just what I was looking for- keep it coming!

There is no evidence that spinning M193 Ball (55gr) in a 1/7 twist barrel does anything harmful to the bullet or its accuracy.

If you're going to shoot iron sights stick with what you have.  Only reason to fit a flat top receiver is to put a telescope on it.  KISS.

-- Chuck

Sounds like a very cool rig, one that many members here would like to build. [8D]

Thanks again guys. I just worked a deal for a used Knights M5 RAS, so it should be pretty sweet once it is all done.