So recently I purchased an ATI Omni hybrid lower and didn’t really think anything about fit and finish of it as it’s polymer with metal reinforcements all over it. When purchased I asked what kind of upper I could pin on it and I was told any mil spec upper will fit fine and function fine. I am just a little on the fence about it being I haven’t shot it yet haven’t had a chance to. Right now I have it pinned on an aluminum 5.56 mil spec pistol upper planning on shooting it this weekend just wanted to get some real world experience with this so has or does anyone have any experience with the polymer lowers on aluminum uppers?