KirkD, welcome.
Many of us load low pressure 2 3/4" hulls for our 2 1/2" chambered guns with good satisfaction. The issue with 2 3/4" hulls in a 2 1/2" chamber gun is when higher pressure loads are used. Higher pressure loads tend to have a higher pressure differential than do low pressure loads.
The 7000 psi recommendation is a sort of rule of thumb based on being conservative with black powder loads and service proof as a guideline. BTW, many BP loads have high chamber pressure; they are not universally low pressure as is sometimes said. There are many low psi 2 3/4" loads in the various loading manuals and web sites. Pick one below 7000 psi (more or less) that you have exact components for and have fun. I shot five-stand last Sunday with a Parker "D" with damascus barrels and can still count to ten on my fingers!!
DDA
