Quote Originally Posted by Emptymag View Post
No difference I'm aware of.

Double check, but I don't think 9mm BCGs have serrations for a forward assist. I'm not 100% sure in that though.
I bought a slick side upper with no FA and no dust cover.

Oh! That's probably the difference on a dedicated 9mm upper - they will have the half door dust cover and that "bumper" thing.
I have no issue shooting mine without one of those and was told it wasn't necessary.

Tomstactical.com had Aero slick sides WITH a dust cover for a really good price.
yeah, 9mm uppers have a smaller ejection port, and a lot don't come with dust covers or shell deflectors.