Bravo Company (BCM)
When the Mk18 was created back in 2001, the extreme pressures and very short duration caused by the short barrel and short dwell time resulted in very quick wear of the bolt carrier groups made for M4 14.5" carbines. A lot of effort was put into making changes by NSWC Crane and by the US Army to repair and to remediate the result of the violent slamming of the BCG back and forth in few short cycles. Over time, the US Military found solutions and today the 10.3" and 11.5" Mk18 CQBR work like a charm. One of the solutions was to improve the extractor spring mechanism in the Mk18 rifle in the early 2000s.
Today, a properly running Mk18 CQBR with 77 grain ammo and an H2 or H3 buffer should perform just fine. But, if you are having troubles, or you just want to be extra sure, as the US Military did back in the early days of the Global War on Terror, an upgrade to the extractor spring set can be a welcome reinforcement.
Bravo Company took the lead early on in providing upgrades to the extractor of short barreled weapons with this three-part kit.