Point 2: The "SOPMOD" extractor "O" ring upgrade was a remedy for the original extractor design used in the M4A1/M4, which was identical to the M16's, using a four coil silver spring and blue extractor "bumper."

Service use revealed that the extractor needed more "bite" in shorter gas systems/carbines to reliably extract spent cases from the chamber. The "O" ring was therefore added to increase the resistance of the extractor so that it would not slip off the case rim as readily.

Colt also developed a new five coil extractor spring with a gold coloration, and a less "squishy" black extractor buffer, and offered several times to upgrade the M4/M4A1 TDP with it.

Nevertheless, for almost ten years, the military didn't really care about this because the M4 family was a low-density weapon system - the majority of the military was equipped with the M16. The "O" ring, five coil spring, and extractor buffer became known as the "SOPMOD Extractor Upgrade."

Once the M4 became being issued in much much larger numbers than ever originally imagined, however, the problem became widespread enough to warrant what is called an "Engineering Change Proposal" or "ECP" to the M4 and M4A1, and the military finally accepted Colt's proposition to update the M4 and M4A1 TDP with the new extractor spring and insert, as well as authorizing the upgraded parts to be used in the M16 family as repair/replacement parts.

If your 6920 was produced pretty much at any time after 2005 or so, it came with the factory with the correct parts, and no "O" ring is necessary, and from your description, you seem to have the correct extractor parts.

The "O" ring was really never anything more than a way to address the issue before redesigned parts became available, once the correct parts became available, they very quickly became redundant, and are rarely ever used these days unless you have to "wrong" parts installed.

With a Colt, again, unless you've reason to believe that someone tampered with the extractor after the fact - you needn't really concern yourself about this, though some commercial manufacturers began selling bolts with black-colored extractor buffers, but that were otherwise identical to the original M16 blue buffer. However, even if you're unsure whether you have the correct extractor parts, extractor upgrade kits are relatively cheap (BCM wants $5 for theirs) to get the right parts.

~Augee