Your gun should have the chamber length marked on the barrel flats in MM, 65mm-2 1/2", 70mm- 2 3/4" and 76mm-3". Sometimes it is just the number, sometimes it will be 12-70. It shouldn't make any difference whether you shoot star or roll crimp shells.
My old shotguns built before there were any star crimped shells pattern just as well with either. I shoot roll crimped shells for my hunting loads and star crimped for SC and skeet with them. Mine are all 2 1/2"/65mm chambers.
