Posting this here because I accidentally deleted my post on the 50k achievement;
While testing different weapons to find out which one kills the fastest, I found that every kill with the Relic Dropshot counts as an assisted suicide and will actually count as both a kill and an assist on the scoreboard.
Unfortunately, despite what the scoreboard says, kills with the Relic Dropshot will NOT count towards the 100k kills achievement, however, they will count towards the 50k assists achievement. As you can see in the clip, this will allow solo players to freely boost without the need for a boosting partner, as long as you have 2 boxes and 5 controllers. At optimal speed, I'm able to get 2,000 assists in a little over an hour.