I got my shotguns when my K\D reached 170, but it doesn't have much to do with it.
It's more to do with Rounds per downs that determines your rank.
A few weeks after getting my shotguns My K\D was around 198, but after getting perma jugg I was deranked. I got my shotguns soon after again after my K\D had gone to 200. But lost them a second time after I got jugg again. The next time i got them was when my K\D had actually gone down to around 195. You see, I lose my shotguns whenever I go down too many times at low rounds. As you know, people have all got different ranks at different K\D's, I have a friend that got shotguns at a K\D of 110. So as a lot of other people have stated, K\D really isn't that much of a factor

Can I add that also you have to have your stats even open a lot of doors, grenade, headshots,miles traced etc. Steven out your stats basically

K/D
171,324/622

Kill death ratio
275.44

I had 378 but slacked off

when i had shotguns i had about a 850.50
K/D
But i got them at about 150-190
I reset them though

I got shotguns at about 190
Now im 500

Kills: 75733
Downs: 160
K/D: 473

But the point when I went from knife to shotguns was in a custom game doing the easy first game of the day. When I went down on round one no kills, downs, or anything brought but my downs went to 150. I think they made it so you need to get X amount of downs for the K/D to show effect. This would stop people ending the game before they die to get an easy K/D.

But that is just my theory.

Thanks for all the info! I've been playing a lot lately for the past week or so.. trying to get up all my stats my doors, miles, grenade kills.. I got my K.D to 168 last night.. I'm going to work on some stuff this afternoon. Thanks for all the help!