I agree with JDW that you should not lengthen the chamber.
You can easily obtain 2.5 inch shells. Further reloading for it is a piece of cake. It either with cut down 2.75 hulls roll crimped or with a press set up to fold crimp the 2.5 trimmed hulls. You can use 2.75 data in a cut down roll crimped hull.
I have found that a cheap drill press from Harbor Freight and the Precision reloading shell vice work well together as does the drill press with no shell vice at all.
You will find that once you get the feel for it roll crimping is an extremely satisfying business.
