Adrenaline Injector is not a good tool and a bad challenge
The adrenaline injector is pretty worthless to begin with; it doesn't really do enough to make it worth using. In fact, it's so negligible that I generally don't ever use it. Then there is the challenge to unlock a spawn beacon. A really important, useful piece of kit to help squad play.
The tracking on the challenge seems to be broken, or the window for getting the kill is so small that it takes forever. Of late, it doesn't seem like they are counting at all. It's not fun and gets the player killed a bunch of times as well.
So the easiest way to do it is to look for a community XP server that has bots and cheat it like that. Come on, EA, this is such a great version of Battlefield, get rid of this stupid challenge, especially for such an important part of kit. Have the injector get unlocked by using the spawn beacon. Have the Spawn beacon unlock from <gulp>, taking objectives! and encouraging team/ squad play.
Adrenaline injector is garbage, the challenge is not fun, and it's a piece of kit that will encourage team play. Please fix this.