So New Jersey finally did what Gen. Gage couldn't, disarm the colonists of thier muskets.
This statement is more accurate than many might realize.
At the time everyone was equaly vulnerable to the musket ball. Organized troops had an advantage, and also had artillery, cannon , and similar equipment, but everyone was still vulnerable to the musket.
The check on power was in place.
Consider now that most modern heavy body armor is designed to resist the 7.62x51mm NATO round. Some even the 7.62.51 AP rounds. If they can resist AP rounds, they can resist even slightly more powerful non AP rounds that will have less penetration.
The 7.62x51 of course being essentialy our .308 round.
If they will defeat a 7.62x51, they will defeat the 5.56/.223 round fired by the AR.
So the .50BMG really is the last civilian legal US military round that is effective against all troops. A round widely available, chambered in robust reliable military arms, that is effective against everyone, just like the musket once was.
(There is others, but they are not military calibers chambered in combat proven and designed platforms, firing a round in widespread circulation at all levels like the .50BMG)
Consider this chart from Pinnacle Armor on what can be defeated by thier body armor:
http://www.pinnaclearmor.com/body-armor/ballistic-chart.php
Level IV
7.62 x 63 mm 166 GR, M2 AP 2880 ft./sec. + 30-0
7.92 x 57 mm 156 GR, mild steel core (LPS) 2415 ft./sec. + 100-0
7.62 x 54R mm 155 GR, steel case, armor piercing incendiary B32 2850 ft./sec. + 100-0
7.62 x 54R mm 184 GR, steel case, armor piercing B30 2850 ft./sec. + 100-0
7.62 x 54R mm 153 GR, steel case, armor piercing incendiary type 53 2675 ft./sec. + 100-0
7.62 x 54R mm 148 GR, steel case, hardened steel core type 53 2850 ft./sec. + 100-0
7.62 x 54R mm 147 GR, steel case, mild steel core (LPS) 2723 ft./sec. + 100-0
7.62 x 51 mm 151 GR, M61 AP 2800 ft./sec. + 100-0
7.62 x 39 mm 120 GR, armor piercing incendiary BZ 2500 ft./sec. + 50-0
7.62 x 39 mm 118 GR, armor piercing incendiary type 56 2500 ft./sec. + 50-0
7.62 x 39 mm 122 GR, steel case mild steel core (PS) 2300 ft./sec. + 100-0
5.56 x 45 mm 62 GR, M855 (SS109 Green tip) 3200 ft./sec. + 100-0
5.45 x 39 mm 53 GR, 7N6 2920 ft./sec. + 100-0
5.45 x 39 mm 57 GR, 7N10 3051 ft./sec. + 100-0
Level V
7.62 x 54R mm 187 GR, steel case, armor piercing incendiary BS40 Classified
7.62 x 51 mm GR, M948 Classified
7.62 x 51 mm 126.5 GR, M993 Classified
5.56 x 45 mm 52.5 GR, M995 Classified
The technology improves every year.
So the .50BMG really is one of the last frontiers of equality, the check on various powers the founders envisioned.
Storm troopers can be employed that will resist common battle rifles in .308 and .223 caliber. The .50BMG still prevails, and even at ranges that make it useful in civilian legal platforms (semi auto and bolt action low capacity rifles.)