Gotcha, I shot a ton of pop-ups both with and without the M68, ACOG, irons, and with goggles until I was in my early to mid-40s. Hitting the distant targets in any unsupported position can be challenging given the equipment proivded.I'd say for the last handful of years conducting rifle quals in the Army, I opted to not pull the trigger on those two 300 yard pop-up targets. Hitting them with pop-up sights after I turned 40 is definitely a NO GO, and hitting them with CCO has lately been a waste of a shot.
I'm not quite ready to try for sub-MOA at 300+ yards with an AR. However, I would like to consistently hit that damn target shooting prone. I don't expect brass sizing methods will matter much in this, but that is where I am coming from.
If you’re using blue reloading equipment, the de-prime/sizing die is full-length.