I have photos of how well my 45-70 and 45-90 group with some shots in the previous hole, so it is not the caliber.

A well mounted scope may refine your sighting, but it also adds more complexity to the issue, so trying it may help diagnose the problem

Good luck sorting things out.

CRS, NRA Benefactor Life Member, Whittington Center, TSRA, DWWC, DRSS
Android Reloading Ballistics App at http://www.xplat.net/