Warface: Breakout

This achievement involves getting a combined 10 kills in a single game with the PKP Pecheneg (Wardens) and AUG A3 Hbar (Reapers). Both are listed under Assault Rifles and cost 5250 credits. These can be customized in the main menu to have the scope of your choice.

There are several strategies which can help, but this achievement is ultimately very skill dependent. Everyone has a different play style so this is more of sharing what worked for me than an all inclusive guide.

First Rounds
The first round of each half don't purchase anything. While the auto-pistol is good, it costs credits and doesn't net many in return. Getting knife kills is the best way to earn credits (1500/kill) in the game outside of round bonuses. In general, if you are unable to buy the gun you need, don't buy anything and go for knife kills, using the default pistol sparingly. With any luck you should be able to get the machine gun by the second or third round.

Play with 1 or more friends
I managed to do this one solo, but for both this and the sniper achievement, having enough credits to purchase the guns on rounds you die is a major challenge. If you play with a friend they can save their credits and purchase the gun for you when you don't have enough, and drop it by holding . If you die they can also pick up your weapon and save it for the next round.

Keeping the game close
Another challenge with this achievement is games going too quickly. If you have the power to keep the score close by throwing rounds either by not planting or defusing, don't be afraid to do so. In a 14 round game there are realistically 6-8 rounds where you will have the gun. Alternatively you could play in hardcore which has more rounds per game, but better opponents. I personally didn't have any luck with this

I hope this helps. If anyone finds a different strategy which worked well for them, leave a comment and I'll amend it to the guide.

Warface: Breakout new season "Cold Sun" added Team Deathmatch consisting 2 rounds of 30 limit kills. Meaning, full size teams of 6 going to 30. Then a second round of first to 30 kills. No gun has a buy limit. Each time you die, you can select any gun during the round. Gun kills carry over to the next round. For this achievement, I had 10 kills with the PKP in the first round and the achievement didn't pop. Looks as though you might have to finish the game. Haven't tested leaving the match after getting 10 kills in a single round. Would play it safe and continue on until the end of game.

This method can be done for the other weapon specific achievements as well.