Heckler and Koch (HK USA) | MR556 A4 | 223 Rem | 5.56 NATO | Black

The MR556 A4 runs the same short‑stroke gas piston operating system as HK's military HK416, which keeps hot carbon fouling out of the action entirely -⁠- the reason it genuinely runs longer between cleanings and shows less internal wear than a direct‑impingement AR. A cold hammer‑forged, cannon‑grade 16.5‑inch barrel carries a lifetime bore warranty, an adjustable gas regulator lets you tune the action specifically for suppressed or unsuppressed fire, and a slimline free‑float M‑LOK handguard with fully ambidextrous controls make the A4 genuinely easier to operate than the original MR556. Real HK416 engineering in a semi‑auto rifle, not a civilian rifle just wearing HK's name.