I just won this one in an auction and from the picture it looks to be a really nice example of this scarce type. It was struck A.D. 312- 313, shortly after Constantine's victory over Maxentius. The AVGG on the reverse refers to Constantine and Licinius. I will take a better picture when I get it and post measurements.
CONSTANTINVS PF AVG
SECVRITAS AVGG
RIC VI London 277