Bullet selection is key to good accuracy. Select a Good Match bullet and do a load work up with different powders. Work your way up looking for that magic powder/bullet /charge combo.
Here is a little work-up I did a few months ago with a new to me Midsouth 55gr Varmint Nightmare. Stock Colt AR-15, 100 yards, 10 rounds each target.
Notice the accuracy node from 25.5gr to 26gr.