What is your shotgun? First, I'd have the barrel mic'd to determine the length of your cone, to se if it's really necessary in the first place.
I have a trio of old (45 yrs+) Savage/Fox B doubles that I regularly shoot, especially the 12 gauge. The cones on these guns is fairly deep, more than the "normally less than an inch" shown in the article you linked. All three of mine only have 2-3/4 " chambers, so no magnums, but I can shoot 50-75 rounds on a clays course and my shoulder feels fine afterwards. I have no issues with accuracy, either, I usually do 20-22 average on a skeet course with a modified and full choke barrel combo.