yuno wrote Thanks for the post, but honestly, no matter how many theories are posted, no matter how many explanations people try to come up with, these things still stay the same:

Tally Marks = Days
KD For a Certain Rank = Unknown

There is no exact KD you need to get to get a certain rank. I have a 51.0KD and I have SkullKnife.

37,522 kills
726 downs
(I've been on this account since day 1 of Black Ops 2)

So KD is still a mystery and if you REALLY want to rank up, watch players who actually get to high rounds on YouTube, and then follow what they do.

You can even try what I did and play Solo. People kept backing out so I hardly ever play in Public Matches anymore.
Also a good tip for a high rank no matter what your KD is:

HIGH ROUNDS (35+ a game)
And don't get downed more than 5 times a match!

It helps.

Just keep playing though, rank shouldn't be your goal. If it is, you are not truly enjoying the game.