I shot several Springfield Armory National Match M1As and never used a small base die. It's easy to see if your rifle might need one. Measure a fired case 1/2" forward of the head, resize it in a standard die and remeasure. If it is smaller now, you do not need a small base die.
In 40+ years of gunsmithing and reloading, I have never seen a quality firearm which required a small base die.
After AA2520, IMR 4895 is the powder of choice for the M1A. But 2520 gives more consistant velocity and meters much better.