I forgot about the inserts, I can't prove the black insert is stronger than the blue, some say it's just to identify rifle vs carbine. But a blue insert will undoubtably be on a weaker rifle extractor spring.
Again get a good kit, BCM, Colt, Wolf or Tactical Springs all have good kits. When in doubt, replace with a known kit.
Action springs or buffer springs can cause problems too. A carbine spring should measure between 10 1/16"-11 1/4". Rifle should be between 11 3/4"-13 1/2". Change every 5000 rounds.
While we're at it, buffer weights;
Carbine 2.9 oz
H 3.8 oz
H2 4.6 oz
Rifle 5.2 oz
9mm 5.5 oz
H3 5.6 oz
Edit to add; the original 9mm buffer is a solid piece and will induce bolt bounce on a 223. The newer versions are a 2 piece affair that acts as a counter weight. Bolt bounce with a solid buffer would or could bounce back faster than the extractor could grab the rim, leaving the carbine out of battery. You can only see it with high speed video but the click will be heard round the world.
What about buffers that have "shaken loose" the filler weight? IE rattle when shaken? Toss?
