JP Components are the way to go, one of the best companies for reliable product. In 3 gun, you want reliability
JP lightened bolt carrier and bolt (bolt carrier has a special coating for a smoother action)
JP lightened buffer and spring
Seekins adjustable gas block
Combine this with a JP, Lantac, Odin, or Surefire competition brake and you have a very flat shooting rifle
Midlength gas system will allow you to optimize on the potential of all these components
Welcome to the sport!