So after intensive testing I came to the conclusion that consuming a Killing Machine does NOT always give you a stack of Bonegrinder. Furthermore consuming a Killing Machine while Bonegrinder is at 5 stacks only activated the Bonegrinder frost damage buff about 50% of the time. And the most alarming thing I found so far is that the 4 set bonus does not always contribute to Bonegrinder. The first Killing Machine proc never gives a stack to Bonegrinder (could be intentional given it’s “not consumed”) and the second Killing Machine is working just as arbitrarily as a normal Killing Machine proc. This results in a high risk of you loosing your Bonegrinder stacks while you get trough the first Killing Machine proc which never benefits Bonegrinder anyways.
From pure data perspective:
97 Killing Machine procs resulted in a total of 63 Bonegrinder stacks and the miserable 6 Bonegrinder activations
Edit: The testing was done on a character with a DW setup and 32% Critical Chance + Bonemaw’s Big Toe trinket (Use: 1591 bonus crit in my case)
Lets hope this gets fixed!