When visiting Verney-Carron they informed me on my question that monos are fine in their double rifles.

So IMO one should be more careful in older firearms than newer, drs and combinations. Myself I will avoid them irrespectively. Monos and H or A thick jacketed bullets. Woodleigh a advised once about limiting the use of their thick jacketed FMJs.

I will avoid monos, H & A jacketed bullets unless forced to by lack of other suitable bullets or Stalinist environmental laws ...

I will happily try the Woodleigh Hydros with RAISED driving bands. Or other similar choices. I will give the hydros a go anyway. See how they shoot and regulate. Cost way too much however.

One thing. Some people say "I shoot them all without any problems!" We checked out such a dr one time. Visible effects on the outside of the barrel per the NE member examining the DR.

Each and all to their own.