I simply took the measurements off my favorite Perazzi international skeet gun. My .458 DR has interchangeable barrels in 20 gauge 3" magnum, which I have successfully shot skeet with, and I have also shot skeet with the .458 barrels, using .410 factory loads with plastic shot columns.

The measurements I adopted were more than simply length of pull. They included drop at comb, drop at heel, and cast-off. Rather than measureing length of pull simply from the front trigger to the middle of the butt, I used three measurements: trigger to heel, trigger to middle of butt and trigger to toe, which is a way of measuring pitch.