How are you adding 14 grains of nock and dropping 2% FOC. What kind of sorcery are your practicing?
Well, a lightweight shaft, light to medium total arrow weight and a concentration of mass in the front of the arrow. I was also rounding numbers. The actual FOC for those two arrows were 17.1%, and 15.0%. With a 125 grain point, a 50 grain insert, and that Halo nock. 41.590% of the total mass is in the first inch or so of the shaft. With the Bohning A nock, it’s 42.957% of total mass in the first inch or so of the shaft. That is taking the insert and point weight, then adding the weight of the carbon for that first inch of shaft.
So, in both cases, around 42% of total mass is in the first 3.7% of the length.
With the Bohning A nock you have 3.5% of total weight in the last inch or so of the shaft. With the Halo nock you have 5% in the last inch or so of the shaft. When you take the difference between those two numbers 5-3.5=1.5. And the difference between the total arrow weight percentages from the other end of the shaft 42.957-41.590=1.367. Then multiply them we get 2.0505%. Which rounds up for a 2.1% difference in FOC.
Or, you can just use software like Archer’s Advantage which will give you the same answer except they do all the math for you.