The only Mk3 upgrade that is currently envisioned which will not be backwards compatible to the Mk2 rifle is the Ejection Port Cover. According to JR Cox, SAI should have the Zhukov Folding Buttstock and Adapter available as an up-charge option in 3-4 weeks. The same applies to the QD Handguard, athough a longer lead-time will be required to bring that particular Mk3 upgrade to market. When offered for sale, both the Folding Buttstock and the QD Handguard will fit the Mk2 rifle without modification. Other incremental improvements, such as extra Picatinny Rail Space for the Buttstock placement, will be incorporated into basic production as "Rolling Improvements" if they are adopted. Those changes will appear in due course on standard Mk2 (and later Mk3), production rifles.