No disrespect intended, but for the neophyte reloader reading this thread it should be noted.....
If you neck size for an AR-15, you'll likely have a lot of feeding and extraction problems.
Ever try dropping a once fired neck sized only 223 case into a .223 case gauge?
As 223 brass has relatively straight walls, upon firing the brass expands and sets quite tight in the chamber - neck sizing only for use in the AR15 is tough on the extractor which why FL sizing is recommended as noted by the OP.
IIRC POF-USA actually uses a 4 grooved chamber,(E-squared) much like/similar to the H&K G3 and FN-FAL, to decrease the likelihood of extraction issues with their new AR15s.
Bolt actions are a different story.
