Just a report on velocities for those interested.
Conditions: 40*F, 4000'MSL, cold guns, PACT Professional at 10ft
Ammo: Black Hills blue box remanufactured .223
75gr Match HP (non-moly)
68gr Match HP (non-moly)
Gun #1: AR-15 carbine
Barrel: 16", mid-length gas, stainless, Wylde chamber
75gr = 2465 fps Avg, 30 fps ES, 5-shots
68gr = 2590 fps Avg, 25 fps ES, 5-shots
Gun #2: AR-15 heavy rifle
Barrel: 24", DPMS .223 Chamber, stainless
75gr = 2634 fps Avg, 26 fps ES, 5-shots
68gr = 2811 fps Avg, 28 fps ES, 5-shots
Summary:
(Ignoring possible differences in chamber tolerances and thus relative pressure levels)
75gr load loses 169 fps in 8", or roughly 21 fps per inch.
68gr load loses 221 fps in 8", or roughly 28 fps per inch.
This was all very unscientific, and I just did it on the spur of the moment.
Comments welcome to aid those who might use this info.