Well - Heres a consideration for the Super Mag Ultra Express models, whatever they're called. As the cartridge length increases, so does the pressure. Upon firing, both cylinder and brass base expand. The cylinder returns to dimension, however the ductile case remains expanded slightly, giving a friction fit.
So the higher pressure models become more dependent upon cylinder polish, etc to overcome this friction. Couple this with Remingtons variable QC, cheap shells, and you can see the issue.
Someone mentioned a new issue beefier barrel - perhaps thats the solution, as it would expand less, causing less cramping of the case.