I have 2 30rd mags with the following stamp on side, 6p199 above 09 /92 also 6p199 above 03 /92
both have center industries floor plates. what do these numbers mean? TIA.

Medic,

6P199 = Center Industries' CAGE (manufacturer code)

03/92 = March 1992
09/92 = September 1992
Manufacturing dates - these are preban mags, anything with a date of 9/94 or earlier is preban.

Post-ban mags are LE/military use only, and have "Restricted Use" stamped on them, along with a date of later than 9/94.

However, watch out for postban Center mags which have the later dates, but no "Restricted Use" markings.

HTH,
Gabe

PS:  Check out the mag FAQ at the top of this forum.