Just thought I'd add this, last night I briefly lost my new shotguns after just a couple of public matches with randoms, first of all I played tranzit, one of the players was using the glitch in the power area and decided to randomly turn off the power at round 15 (after watching it back in theatre). I was stuck at the diner with no turbine so couldn't get back to turn it on. The other 2 guys went down shortly after, and respawned with me. I was able to revive them everytime they went down, and I even earned the quick revive upgrade from that game, but we all ended up downing at farm on round 18 on the way back to the power. So even though I feel I played pretty well, my K/D for that match was only around 75.
After that I went into town survival, and a stupid mistake meant I went down on round 5. I waited to get revived, but everyone else just left me to bleed out despite it being near the end of the round. I thought, if they can't revive someone on round 5 then we have no chance, so once I started spectating I quit. I really hate it when people rage quit, and I guess I deserved to lose my shotguns for that, and thats exactly what happened. My K/D had fallen back to 195. It took me just one game of solo Tranzit to round 32 to get them back though.
I don't know how useful any of what I've just said is, but for me at least it appears that once my kdr falls below 196 I go back to the skull with knife. I know it's not the same number for everyone, but as it only took one game to go back to shotguns it doesn't appear that you have to reach high rounds on back to back matches, assuming the rest of your stats are good that is.