Originally Posted By: Drew Hause
Scroll down about 1/3 here for details of Bell's study
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit
Bottom line: Shooting 2 3/4 shells in 2 1/2 chambers does make them produce more pressure-but in most cases it is less than a 1000 psi increase. I see no reason, related to safety, to modify an original 2 1/2 chambered gun to shoot 2 3/4 shells, if the 2 3/4 load you intend to use would develop pressure that is safe in that gun, when fired in a standard chamber!

Depending on the gun and barrels, 1000 psi may matter however.


Good reminder, Drew. We tend to remember Bell's article as telling us that, on average, the increase is only a few hundred psi. I went back and reviewed the article some time ago. Average increase for 10 loads he tested: 709 psi. However, 4 of the additional pressure readings vary from 891 to a high of 1216 psi. Thus, if you're going to reload 2 3/4" shells for 2 1/2" chambers, you do want to build in an additional safety cushion. I'd say 1500 psi should keep you on the safe side.