Back to the forcing cone issue. Personally I see little if any advantage to long forcing cones & some disadvantages if one desires to shoot some card & filler wads. It must however be admitted they have been highly touted as a cure-all for everything from poor patterns to excessive recoil & many bought into the hype. The highest pressure point in firing a shotshell is inside the chamber, the pressure is actually falling by the time the cone is reached. In the Vast Majority the thinnest point is at the juncture of the chamber & cone, with metal thickening as you go down the cone. As mentioned earlier even with a cone of around 1˝" long the thinnest point is unchanged from that juncture. With the possible exception of a few very rare cases there is thus little factual evidence that lengthening a cone will in any way weaken the barrel.
The same thickness as at the chamber/cone juncture will not be reached for several more inches down the barrel where pressures are still lower.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra