The Korean made magazines are as good as USGI magazines are. After all they have had over 700,000 carbines they had to have magazines for that worked as well as USGI magazines do. These magazines are marked as JimB said with a large U and some are also marked with UU. Both markings can be found on the 15 round and the 30 round magazines. In general the after market magazines made here and in China are junk.