Currently Master Hunter can be built by any unit that produces enough

only. I think I set it at 6

or more. I felt that that early in the game this was the only consideration people would give for what a master hinter did. I may have changed my mind mid way through and said 6

or 6

.
I keep meaning to go through all the animals and make sure I have the amount of food and hammers from a kill, and butchering consistent but I never get the time. Food is just edible meat but hammers represent antlers, horn, bones, teeth, claws, fur/skin etc. so it would be good to look at separating that so there would be a bit more technology related variation. Antlers for example provide more hammers because they were used as picks to dig out dirt and stone, small bones were used as needles and awls and so on.
If you wanted to look into that I would appreciate it.