iirc; Eugene Stoner, originally designed the rifle, the (AR-15), m16a1 is the military designation, firing a 223/5.56 cartridge out of a 20” barrel, with a 300 yard/meter engagement distance in mind and designed the rifle to be used in the jungles of Vietnam. Historically, the fielding unit with the most amount of ammunition on their person, won the engagement. So the cartidge grew smaller from the 30-06 from WW2 to 308/7.62x51 to 223/5.56 for infantry man.

Drawbacks were discovered that the 20” barrel gets in the way sometimes, so a shorter rifle was produced, I think 14.5” barrel, the M4.

More drawbacks were found out early in Afghanistan or Iraq, where rolling hills and mountains, could easily turn the battlefield into a 700 yard/meter plus engagement in a blink.

Black Hills was tasked with producing a match grade (accurate/consistent) cartridge that could be used in the AR-15 platform. A new rifle, or upper receiver was designed and produced, the Mk12 Mod 0, an 18” Compass Lake heavy barrel, with an OpsInc12/Allen Eng. AEM5 suppressor; these early uppers were mounted on m16 lower receivers.

This new match grade cartridge (the military ammo designation: mk262) is a 77gr SMK hpbt (Sierra Match King Hollow Point Boat Tail), which is heavier than the originally designed cartridge savages before, a 55gr fmj (full metal jacket) bullet. This new round in the new accurized rifle killed many people with precision. Many units were trading their gear/food rations for this ammo to use in their regular service rifles.

This new round, that is this post, is designed to shoot even faster and flatter. It does baffle my mind that they did not decide on going with 6.5creedmoor…

I really wanted to see General Dynamics and 6.8 TVCM polymer casing cartridge win, but the material has its constraints and big army has very strict testing protocol for ammo, which needs to survive in storage, a huge temperature delta.