Originally Posted by
CarbonScoring
What billet upper are you going with? If it's a Mega, you might have issues. I'm not positive (someone else might be able to clarify), but the Mega billet uppers don't usually work with Geissele rails without modification.
I'm building a Mega billet rifle right now, and I decided on the Parallax Tactical M-lok handguard because the Geissele rails require machining of the upper receiver.