Remington used to show an explanation in their Ballistics Information section for this loss. They start with a 24" barrel as standard and divide the lose by Muzzle velocity range.
2000-2500 10ft/sec per each 1" below 24"
2500-3000 20ft/sec per each 1" below 24"
3000-3500 30ft/sec per each 1" below 24"
3500-4000 40ft/sec per each 1" below 24"
Remington in their literature states that these values were determined in test barrels in the lab but should represent the approximate lose in performance in actual rifle barrels. I personally don't know much game that can read ballistics tables where it would make very much difference in thefield. I kinda believe if the chronograph had never been invented there would be many MORE satisfied handloaders. Never having used one or seen the real necessity I am probably jaundiced in my view.