Picked up some brass a while back. Headstamp says PSD and either 1 5 or 1 4. I know that PSD is for Poongsan Metal Manufacturing Company Ltd., Seoul, Republic of Korea (http://cartridgecollectors.org/?page=headstampcodes#P), but what do the 1 5 and 1 4 mean? Since the primers were crimped, I'm assuming 5.56x45.