Great thread, this one ...
The 20" SP1-type ARs actually have more advantages than what the "cool kids" might think with their 16" carbines, which have every manner of optics, flashlights, bipods, and other do-dads hanging off them, and end up weighing 15lbs.
These old school, pencil-barreled ARs were extremely accurate, maximized the velocity of that era's 5.56mm ammo with their 20" tubes, and were (and still are) comparatively light-weight if you have to hump them around all day.
Yep, .. you take one to the range on a gorgeous day like I did for an afternoon of shooting - and, well, let's just say, it feels like
1965 all over again.
And, trust me, I'm a dude old enough to remember
1965.
After 200-rds on a hot day.