Hi, I'd just like to share some of my experience with the ranking system. Some have said that it has to do solely with KD, others have said you just need to do consistently well (30+) three or four times in a row to get shotguns. Clearly we haven't figured out exactly how the system works, but maybe my experience will shed some light or promote some new theories.
About a week after the game came out originally, I was a regular skull, still unaware about the whole "get your K/D up to rank up" thing. I have a friend who I play consistently with, and we're of pretty similar skill, with me being possibly slightly better. I had played more than him (unsure about K/D at the time), so I believed that I would rank up to the skull with knife. One game we played with four people on Tranzit, and we did OK (Got to round 17 or 18, public match which was the first time we had it ranked on the leaderboards, decent for one week in). My friend ended up getting the Skull with knife, even though I had played more than him. I was kind of disappointed, and so the next day I actively tried to do very well to get the knife. I played one good game of grief which I did better than two Skull Blue-eyed knives (pretty rare rank at the time) and got no downs. At the end of the game I found that I had knives (again, no idea of K/D or total kills at the time).
Flash forward to last night, about a month later. Both my friend and I had been trying very hard to play well and get our KD up, because we had heard that it helped to determine the rank. I cared more about KD and I played a lot more than my friend, but I found that I couldn't rank up. I broke a 200 KD while my friend was still at 130 or so, and still did not have my shotguns. I play a lot of grief, and even after winning 5 or 6 games in a row at above a 200 KD, I had not received the shotguns. Last night, I played exceptionally poorly for whatever reason. I disconnected from a game of grief after getting a down, counting for a loss and a down. The next game of grief I won, but I did very poorly and had less than 100KD with 5 downs.
The next game I played a game of 4-player survival on farm (with my friend and two other skull ranks). After playing for three hours, we made it to round 30 (top 1k leaderboards) and suicided because we were bored. I ended up with about 1800 kills, but I had 11 downs, so again I brought my KD down. My friend had about 1600 kills with 8 downs, so his KD wasn't great either. At the end of the game my friend with less than a 140 overall KD ranked up to shotguns! I was very surprised and kind of disappointed, because my KD was a lot higher and I had beat him in kills, revives, and headshots during the game. We tried to figure out if he had some special stat that was higher than mine, but could find nothing.
This morning I decided to once again go for shotguns, so I played a game of solo farm survival. I ended up (again) doing very poorly, only getting to round 22 or so with 4 downs and less than 800 kills, once again bringing down my KD. At the end of the game I was surprised to see that I had ranked up to shotguns.
So, once again I ranked up exactly one game after my friend ranked up, months (and many zombie games) later. It would be a pretty big coincidence for that to happen just as it had a month ago. In addition, I found it weird that I ranked up after three games of zombies which I actually performed worse than my normal, and my KD actually dropped from about 208 to 202 over the course of the three games. So, I ranked up to shotguns from three BAD games directly after my friend had ranked up, just like months before.
Perhaps the ranking system has to do with the ranks of the people who you play with, or the ones on your friends list? I know it sounds really far-fetched, I don't believe it myself.
Sorry for the long post. If anyone can make any sense of what happened, I would appreciate it.