I got this using the Chinese NC-31(the free tier I tank), and I recommend using this tank for most of the new achievements. Using the standard gun, and depending on how much silver you have, you'll want to buy a few shots of the Armor-piercing shells, or the High-Explosive shells.
To purchase these shells, highlight your tank and press
to open the upgrades. Select "Supplies," and you'll be brought to the purchasing screen. To purchase ammo, highlight the shell you want and press right on the d-pad (
) until you think you have enough. Probably shouldn't need more than 5.
If you have a lot of silver, press
. This will change the currency of the Armor-Piercing shells to silver instead of gold (unless you want to spend your gold, then have at it). These shells, as the name suggests, have a high penetration rate, increasing your chance of causing damage. If you don't have a lot of silver, you can buy the cheaper, High-Explosive Shells. These have a terrible penetration rate, and you should really get the other ones if you can afford it.
When you've bought what you believe to be a sufficient amount, plunge into the game. When the match starts and you have chosen your victim, bring down his health as much as possible with your standard gun. When the health is low, switch to your other shell by pressing
. If the health is low, you should be almost guaranteed a kill with the Armor-Piercing shells. The High-Explosive ones though, not necessarily. Now, these were the ones that I used, but my opponent was an LTraktor, and those aren't exactly known for having high armor. remember, what ever shell you use, try and hit either the back or square on. You'll want to minimize the chance of ricochet, especially if using High-Explosive, so don't fire at an angle.
Once you've done that, you'll need to get another kill with your standard gun. You could do this first, but I recommend using the premium ammo first while you have more options for targets. The NC-31 has a fantastic stock cannon (high damage, high penetration, fast reload) so this shouldn't be too hard. Just use the same tactics and you should be good.
Also wan to note, there is a delay. The achievement popped almost 10 seconds after i had made the requirement, so don't be nervous it it isn't instantaneous.