I took out my P.O.F. p415 (HK 416 clone) with Barska Electro Sight red dot optic. The red dot sight works pretty well, and is sighted in at about 25 yards. I used PMC 55 grain ammo and got pretty good results. I really like my P.O.F. p415. It's accurate, easily modified, a bit on the heavy side, but really a great rifle.
It has an "18 heavy barrel and a great HK style front sight. I use a Stag Arms lower with the POF upper and I've had good luck with just about all the mags I've used. I bought some Tapco mags for $10 a piece and they work great so far. I really like the Korean HK 416 knock-off magazines as well. The POF p415 upper is a bit pricey, but if you want quality and accuracy, POF is the way to go. If I had the money, I'd like to get one of their 7.62x51 (.308) models.
Here a video of me shooting it:
Johnny 5.56: P.O.F. p415 (HK 416 clone) with Barska red dot