In these rifles (m305 or any other M14 type) my suggestion to folks is if your headspace is over 1.640" , use 7.62x51 Nato spec ammo only.
If your headspace is tighter than 1.632" ONLY shoot .308 commercial spec ammo. The few hundred norinco/poly rifles I've measured with the clymer gauges over past few years. Have headspace averages between 1.636" and 1.638" , widely regarded as Safe for BOTH.
My order was confirmed, no tracking yet.... But I'm sure it'll be along soon enough