The origin of accurizing the AR and the M4/M16 platform can be credited to GWOT, seen in the MK12. Prior to the MK12 Special Purpose Receiver AR’s, even shot for accuracy in matches like Camp Perry, were still very much an M16A2 standard. “Accurizing” the rifle was accomplished through weight and match grade iron sights.
The MK12 SPR was the gap span measure. Covering the span between dedicated sniper platforms like the M24/M40 (later the M110) and the M4/M16 service rifles. The MK12 offered more accuracy and precision, suppressor capable, greater observation capability, and a minimized rate of fire decrease over an optimized 5.56 effective range. The SPR closed off the glaring vulnerability using a bolt action as a primary would induce without removing a precision tool from the sniper team’s hands.
Instead of a spotter, a trained sniper also, being constrained to limits of an M4 with at an ACOG (at best), the MK12 allowed them a platform that nicely bridged the two worlds of precision and direct action. The sniper team could reach into either at will while equipped with the weapons.
In the Designated Marksman role it allows a precision tool to be added into the fireteam or squad mix. Shifting the ammunition loadout of a rifleman or severely altering their ancillary equipment is not necessary with a MK12, making it a literal drop-in solution with very little extra training necessary to utilize. There is often enough Mk262 ammunition in operation for sourcing it to be easy and obviously M855A1 or Mk318 will run in the rifle too.
Now we are seeing more and more optimized features come out on the AR’s as standard. Freefloated barrels and handguards, optimized gas systems for suppressed and unsuppressed use.