One of Webster's definitions of "consistent" is "reliable, steady." When I think of someone who consistently kills mature bucks I think of someone who kills one at least every other year. Because, in all honesty.....someone who can kill one every 2 years most likely had a chance on the "off" year. Someone who can reliably kill one has their opportunities every year. Just because they didn't connect on a given year could be a lot of things. Perhaps they just didn't see one that met their standards, or....perhaps they had a shoulder injury.

Anyway, the short answer would be every 2 or 3 years.