I relied on an old macro from yellow for MG36 and just changed recoil values for MG249, works fine
So i canīt really tell you why it is/was 120ms....usually you can calc ms by shots per second (see symthic for data), but it is just some rough value, you still need to finetune by try&error.
Like 800RPM: 800/60sec=13,333 Shots/sec ---- 1sec=1000ms, so 1000ms/13,3333=~75/76ms per shot. Experience shows, you should use half that value, so 76ms/2=38ms intervaltime. But you should add some ms for the game to work the shots as intended, so give maybe 40-42 a try. Finetuning is easy after that point (just add or substract some ms and see how if the clip gets emptied flawlessly).
For recoil it is always try&error, since this completely depends on the players ingame mousesens.