M855A1 is copper core. Lead free was a requirement as lead contamination from ranges was becoming a problem. See: https://www.army.mil/article-amp/106710/pica

M855A1 is copper core. Lead free was a requirement as lead contamination from ranges was becoming a problem. See: https://www.army.mil/article-amp/106710/picatinny_ammo_goes_from_regular_to_unleaded https://www.army.mil/article-amp/106710/picatinny_ammo_goes_...