Hey now.

I just fixed a friend's rifle that was having troubles with infrequent failures to extract. It would try and get rid of the fired empty casing but the casing remained in the rifle long enough to prevent a fresh round from feeding into the chamber. The rifle jammed up. This trouble was hitting the rifle every so often (1 time in a 100 rounds then 2-3 times the next 50 rounds.)

I had originally told him to clean the chamber with a good brush and solvent. He also had it well lubed and was using good quality factory ammo (not Wolf).
The rifle was a brand new 16 inch barreled upper with M4 feed ramps, chrome lined, has the proper extractor spring and black colored insert.
Still had troubles.

I finally got the rifle for him today and went over it to find the trouble. After pouring over the rifle, I found the extractor groove was slightly undersized. The groove was clean and sharp, but measured .062, .0625 & .062 inches in width. Darn thing was just wide enough to work most of the time, but when a slightly thicker case rim was encountered, it didn't get enough of a grab on the rim to do its job.

Compared it to a known good running extractor, measured .064, .0645 & .064. Also compared to a well used but 100% running Colt M4 extractor, measuring at .065, .065 & .065. (I wonder why the Colt part was so consistent in size.....)

Traded out the small extractor for a slightly wider (.064) and guess what happened? The rifle ran flawlessly!

So, if you run into the same trouble with FTE in your rifle, take a look at the extractor groove and measure to ensure its not too small.

Anyone want to share the measurements on their extractor grooves? Maybe my finding is compete BS,,, maybe Dano can weigh in on this?  

The rim on a 223 is only around .045 thick. I have plenty of milled mil spec extractors that work fine and only measure around .062.
Not saying changing the extractor did not fix your problem but I doubt it was caused by the width of the groove.

Thanks for the measurement.