The best way to get an ACE legit, is to try and get the most XP for a match. Play the tank you are good at and try and get as many kills and dmg hits.. also try to be active in the match spotting and getting assist points.
I am not 100% sure when the weekly Mastery badge reset are, prior to the last few patches the servers reset the Mastery Badge every Thursday after the reboot 3AM EST time. The last patch, the servers seemed to reset the Mastery badges every Tuesday morning after the reboot.
EDIT:by the way, what i meant by resetting, is not for the individual players mastery badge but the reset of the high scores accumulated for the week or what ever length of time. ie easier to ACE mastery ... you do not need such a high base xp.
trust me, play any one of your tanks right after a major patch or the weekly server reboot/save, and if you happen to be the first or the first few to do well in that tank.. you get M mastery.
I will confirm after this week which is the exact day of th eweekly reboot/reset. Just like the weekly reset, any patch updates usually reset the mastery badges.
With that being said, once you know the server you play one mastery reset day, simply play any tank you are good at and have a good match and your will easily ACE that tank for the cheevo.
I noticed that even after a few days after the reset, some tanks are not played very often by many and can easily net you an easy ACE for the cheevo. I found than many tier II-IV of any country lacks the player base using those tanks since it is so easy to grind past those tanks and most players simply sell them to grind the next tank in the tech tree or make room for the higher tier tanks. Use this to your advantage for this cheevo.