ACE COMBAT 7: SKIES UNKNOWN

This achievement may seem like a nightmare, especially when facing opponents who perpetually fly the Wyvern or the Raptor, but with the proper strategy (and plane) it's actually a lot easier to get than you think.
The correct plane depends on your play style: I would recommend using something fast and maneuverable or at least a plane with plenty of flares.
For your play style, we'll focus on the Nosferatu (DLC plane), the Raven (DLC plane), the SU-47 "Berkut", the YF-23, and the F-15 model that has access to the SASM. (I've personally won Battle Royal with all of these planes and more, but for now, we'll focus on just these).
All of these planes have different play styles according to them so at least one of them should appeal to you:
The Nosferatu has access to the ADMM, which can fire up to 12 missiles at once. A good strategy is to fly into the furball, turn sideways, and fire off every missile you can get a lock-on for. If you don't get a kill, it's a sure chance that you'll get at least a few hits. After firing, dive down for cover if ground is beneath or up into cloud cover if on one of the water maps. Stay in cover until you've reloaded completely, meaning all 12 missiles are ready to fire again and repeat.
The Raven has access to the deployable drones which, while slow to fire, will ALWAYS get you points provided your target doesn't fly into cloud cover. You won't have very many of them even with mods so make them count. The Raven also has access to a PLSL as its machine gun weapon with infinite ammo, though it is useless in the clouds as well. (The Raven also has the QAAM; see below).
The Berkut is one of the higher-end planes and has access to the QAAM, arguably the best missile in the game. This one is a straight-up bruiser plane, so expect to be in the thick of it quite often. It's fast, agile, and very maneuverable, so fancy flying comes very easily with this one. I would recommend focusing on single, slow-moving targets with the Berkut as the QAAM can make mincemeat of them easily.
The YF-23 is a stealth aircraft and has access to the HVAA, probably the fastest missile in the game. If the earlier planes are meant to be "front-line" planes, imagine the YF-23 as a sniper. A good strategy is to fly as high as you can, point your nose down, get a lock and fire. Most players will likely believe the missile to be heading for them on the same plane and won't be expecting it to come from above! Also, if an aircraft is making its way back into the combat zone on a straight path, and you fire at it straight-on, it'll most likely be a kill. Maintain your altitude as most aircraft won't be able to find you even from the kill cam, after all, it's a stealth plane!
Finally the SASM F-15 isn't necessarily good for kills, but it's great at mopping up! Most SASM shots WILL score a hit, netting you a few points but kills are worth more. Take opportunistic shots with this craft as it will be able to stay in the fight longer due to having more flares than most craft. Targets with little health or that are slow-moving are a NUMBER ONE PRIORITY with this strategy!
(If none of these aircraft work for you, I would also recommend a QAAM-equipped F-22 Raptor and a EML-equipped Wyvern, which WILL NOT miss if timed right).
Hopefully one of these craft will help you get this achievement!

Good news is that this can be done in private matches.

If you can double box this is easily done solo, if not all you need is one other person to start a match in BR.