Call of Juarez: Bound in Blood

You have to disconnect from XBOX Live (as your clock is automatic when connected)

Simply change your console clock to 11.55 or 12.00, load the game up. I used Chapter 4 as you start shooting enemies straight away, within a few minutes the achievement should pop. Connect back to XBOX live and your clock will go back to normal.

When I first read the achievement text, I presumed High Noon was some kind of special ability that one of the characters had. Turns out, it's just a lousy translation from Polish.

To gain the achievement, you must kill 4 enemies between 12 noon and 12:15 PM local time in either the campaign or in online multiplayer. You can accomplish this in one of three ways:
-) messing with your console's time zone until you're near/within the required timespan;
-) disconnecting from LIVE and setting your console's time directly (obviously no multiplayer or achievement timestamp this way);
-) just wait until you have some free time at 12 noon someday.

What I ended up doing was load up chapter XI on easy, let Seeing Further row the boat until the group of Navajo lookouts on the left came into view, then paused the game until the clock on my Guide said it was 12:00 PM. Unpause, lots of shooting, achievement unlocked. I'm sure just about any chapter will do, this was simply the first one that came to mind with enemies near the beginning.

Checkpoint reloading does count the kills just like the game's other achievements. If you kill 3 guys and figure the firefight you're in is a good spot, just reload the checkpoint and you'll unlock the achievement after killing the first guy.