It varies, if you know what it was the first time you got them, it should be somewhere around there. 160 seems to be the magic number for some people around here...
I think it also depends on the number of total kills you have. I started my shotty grind when I had about 150k kills, it took me getting my k/d to over 220 before they popped. That was finally around 230k kills.
Yeah I didn't get mine until an exact 240 kill/down and 280 kill/death, but if he got his around 150ish k/d it probably won't take that much grinding for him to get them back. It seems like the algorithm works differently for each player depending on all the stats working together.
I saw a kid get his shotties with a K/D of 114 the other night. He'd only just got past 20000 kills aswell. The other stats really do play a big part I think.