CRK-A5 is a bundle of the superb Vltor A5 systems (A5 spring, receiver
extension, and buffer) with components from Forward Controls Design (CNF
and ESF). We have also added a few options that are related to the carbine RE, such as the reinforced buffer retainer, retainer spring (RBF), and carbine stocks.
Those that know us will also know that we're huge fans of the Vltor A5 (and anything Vltor, for that matter). Vltor's A5 system is without a doubt, one of the most beneficial improvements one can make to his AR. It transforms the short and sharp recoil impulse into a soft and gentle push, akin to that of an AR with a 20" barrel, rifle length gas system, spring and buffer. The A5 also makes the AR more reliable, it offsets the violent actions of a carbine gas system, and it is far more tolerant of the sometimes finicky AR in semi and automatic fire.
Note that due to the shortage of A5 components, CRK-A5 often will not have all RE and buffer options available.