MR556 A4 Upper Receiver Kit – 16.5″

The 16.5-inch upper receiver kit for the MR556 A4 in 5.56×45.

What an upper receiver kit is: the complete upper half of the rifle — barrel, gas system, bolt carrier group and handguard — without a lower receiver. It lets you change calibre or barrel length on an existing lower rather than buying a second complete rifle.

Fits: MR556 A4 lower receivers. Not compatible with standard AR-pattern lowers — confirm before ordering.

Worth knowing: at 16.5in this is rifle-length, so pairing it with a stocked lower does not create a regulated short-barrelled configuration. That makes it the simpler choice of the two MR556 kits. The shorter option is the 11in kit.

Browse the upper receiver kits range, or upper receiver parts for individual components.

Firearms and regulated components are not sold directly on this site. Listings are informational and link to the manufacturer web shop or an authorised dealer. Upper receiver rules vary by jurisdiction — confirm what applies where you live.