Is the gun nitro proof? What were the wall thickness measurements in the chamber and forcing come area? Is it a game gun, or something of heavier construction? These do have a bearing on whether I'd be happy to shoot it with smokeless.
With all the caveats you've identified: any loads that stay in the 5000-7000 psi range ought to be ok; the case length is not an issue - roll crimp the top instead of the fold/star crimp of a 2 3/4" case.

Last edited by cadet; 02/27/12 07:42 PM.