NOTE: Corrected the brand of powder.
I finally put together some new test loads for .223 for one of my AR-15s. Components were:
Accurate DP 2200: the older lot from the 1990s, not the newer lot from, I believe, 2010.
Barrel: 20-inch, DPMS, 1/8 twist, with muzzle brake.
Brass: Winchester
Primers: CCI Small Rifle Magnum
Bullets: Sierra 69-gr Match King
Loads chronographed using an Oehler 35-P.
Briefly, the charges, mean velocities and standard deviation of each 5-shot string were:
19.0 grains: 2414 fps, SD 6
19.4 grains: 2476 fps, SD 10
19.8 grains: 2533 fps, SD 19
20.3 grains: 2584 fps, SD 14
The good news is that the 19.8-grain load produced a very nice 1.5-inch, 5-shot group at 300 yards.
The bad news is that this lot of the powder is so fast (faster than AA2230) that it didn't produce enough barrel dwell time to cycle the action, even with the adjustable gas block open all the way. This is unfortunate since I have about 28 pounds of it.
Interestingly, the powder did work in another AR-15 before I changed the barrel. I'll have to try that one, again.
Richard