As the title i am planning a AR9 build, i got all the parts including a TNArmsCO 80% lower i got on sale for like $23. Partly finished the lower but now second guessing if it ok to use for a AR9 build some people tell me that polymer lowers can't handle it.... I also got a P80 556v3 lower i used for my AR15 Other build i put about 40rds through with no issue...