I actually played three rounds of "Boooooom Snipes" last night (12/20/12) and I am pretty sure that the event was from the 19th to the 20th. I did not, however, get a ribbon for it (just like the previous "Hardcore Weekend".
Again, I started to play Gears 3 back in late May, so there is no way I could have had the ribbon from before. So even though I didn't get a ribbon, I can absolutely confirm that "Boooooom Snipes" was up on Thursday (12/20/12)
Edit: I just finished playing "This is my Rifle" and I got another Judgment ribbon. I did not get one for "Boooooom Snipes" (on Thursday) or "Hardcore Weekend," but I did get one for the others. Weird. Maybe ... uh, nah, I got nothing. I have no idea why some of the Gearsmas events are giving me ribbons and some are not.
Last edited by Silicon Iceman; 12-22-2012 at 12:47 AM.