Here is Eastman's guide to field judging....
First determine the distance between a buck’s ears, ear-tip to ear-tip across the forehead. This measurement will be used to evaluate inside spread width. Unfortunately mule deer ears will vary in length from 9 to 10 inches depending on the unit or state. In addition some bucks in certain units will have bigger heads adding to the ear tip to ear tip length. In my experience Wyoming and Idaho mule deer, tip to tip, will vary from 21 to 23 inches. However in Colorado and Utah ear widths will be 24 to 25 inches. I guarantee that there will be exemptions to the rule in all western states, but this is a beginning benchmark. Saying that, you need to gather your own ground knowledge for the units you personally hunt.
My first rule for judging is what I call “good fronts will make up for bad backs.” The “fronts” include the three measurements:
1. The inside spread (determined by comparing it to the ear-tip to ear-tip length)
2. The length of the G-4 points (points coming off the main beam)
3. The length of the two main beams (visually take the length of an ear, end over end, up the main beam to come up with a sum total. Three ears = 27 to 30 inches)
It’s easy to evaluate the length of a G-4. A long G-4 can almost reach as high as the back tines in length. A short G-4 ranges from 4 to 6 inches in length. Remember long G-4’s are a sign of a good main frame.
These 5 measurements (the inside spread, two G-4’s and two main beams) in inches will usually add up to 49 – 60% of the bucks total rack score. So this is the most important section of a racks score.
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Here is Eastman's guide to field judging....
Unfortunately mule deer ears will vary in length from 9 to 10 inches depending on the unit or state. In addition some bucks in certain units will have bigger heads adding to the ear tip to ear tip length. In my experience Wyoming and Idaho mule deer, tip to tip, will vary from 21 to 23 inches. However in Colorado and Utah ear widths will be 24 to 25 inches.
Anyone measure the length and tip to tip width of the ears on ND mule deer? Or have used this method and verified it with actual deer in hand?