Reiska wrote:
Now, I would like to know what it takes for the AR to cycle..
gas volume. thats what cycles AR's (in addition to pressure anyway). not enough gas produced = fail to cycle. thats how the bolt moves.
which most really fast pistol powders do not produce a lot of. you get a quick pressure spike but its not sustained, and the powders do not produce a lot of gas as they burn - or enough to move a BCG correctly anyway.
those powders burn formula's are designed to operate a blowback system - or not operate a gas system at all (wheel guns, etc etc) - not gas impingement systems. you can do some fun stuff in bolt guns with them, but nothing that requires a system to cycle like an AR does.
as such - the powders that tend to work well are usually classifed as magnum pistol and faster rifle rated powders (like your N120). stick with powders around that burn rate of the typicals you see used in this caliber (h110, n110, lil gun, 4227, 1680, shooters world blackout, shooters world socom, etc etc etc) and you'll be successful. venture too far off the farm and you'll get a failure - and potentially get into the realm of dangerous quickly.