Well there are a few things to check out right away.
Bushmaster has had some troubles getting the barrels indexed perfectly, and the problem will show up when you atttempt to zero the iron sights. If you end up with excessive windage adjustments left or right, then the barrel is likely slighty mis-indexed.
Hopefully you have a carbine that zeroes dead on center! 10 clicks left or right would not be good in my opinion.
Bushmaster also has an issue that may require a front sight post that is .040" longer than normal to allow for sufficient upward adjustment when using some types of removeable carry handles and/or Back up iron sights (BUIS).
If you have gotten past the first two issues and the rifle operates normally as far as feeding , firing and extraction, Then I would look into making sure the bolt carrier key is properly staked and if the buffer extension lock nut has been staked to prevent any loosening of these components.
I would recommend that you do all this BEFORE you start with the customizations you may have in mind. It just prevents doing a bunch of mods to a rifle that has not been "vetted" and needs a trip back to the factory.
If you make a bunch of changes before you know it works right, then it makes it tougher to figure out where the problems may lie.
Hopefully you will not have any problems to fix, but if you do let me know and I will help.