I'm not saying the KJW is perfect, if you have the V1 bolt, stock up on elastics... and the V2 bolt wears down the bolt catch a lot faster. The RA-Tech NPAS is complete crap though. While the Cradle Velocity Adjuster is great. Not many aftermarket internals available for the KJW, but it doesn't need many.
KJW Mk18 MOD1 BLOCK 2 - Well VSR-10 - Les Baer Ultimate Recon