I want to put an Collapsible Buttstock on one of my ARs but i have a problem with the buffer tubes.I understand that it is a difference between mill spec and Commercial buffer tubes but i cant seem to figure out if the difference only apply to the buttstock i can mount to it, or if my rifle can use only one or the other.So is there a difference in the part that fastens to the rifle? If so,does anyone know what kind of buffertube is used on rifles from Olympic Arms and Bushmaster? Sorry about my poor english, not my native language