I've been using whatever powder is readily available.
I recently loaded a bunch of 55gr FMJ, using 25 grains of IMR 4320. Not the best powder for that caliber, but it gives me almost the same POI as the "el cheapo" steel cased Wolf ammo, and military surplus 55gr loadings I was using, prior to the ammo "shortage".
I was using a Hornady powder thrower, and every 10 rounds, I would check the charge weight. I actually found a variance of between 24.5 grains to 25 grains. I found for the AR, this variance isn't a deal breaker. If your looking for more consistent accuracy, you'll want to weigh each charge.