There is a difference between sharply tapered and stepped forcing cones. The old guns shooting fiber wads had short, or sharply tapered forcing cones, to help seal when using fiber wads. I had a Parker 10ga that had a step at 2 5/8" in. There were no tapers. I believe it was for brass shells. For that reason I cut the shells at 2 5/8. All the rest of my shooting short chamber guns [ 12ga ] I never cut the shells, just shoot 2 3/4". Sherman Bell did do test with 2 1/2" chambers using 2 3/4" shells. Most of the time pressure went up around 500psi, and once around 900 or a 1000psi. I don't have that article right in front of me but will try to look it up. I have measured a couple of my SxS Remingtons and they all had 2 9/16 chambers. I hand load and keep pressures down around 7500, so shooting longer shells in short chambers has never bothered me. I just quite measuring chambers.
