Jani, as much as I love the .22 WRM, the conversion from CF to RF can be expensive and vexing, might be especially so in a double rifle. It takes some serious geometry to shape the liner so that the CF firing pin hits the rim of the RF cartridge. I've seen it done, but not in a double. Actually changing the pins from CF to RF is feasible but VERY expensive unless you can do it yourself.
I like the conservative suggestions to handload until you find a reasonably accurate load, or let it alone. Many of the ".36 cal" rook cartridges use heeled bullets and can be made to shoot by using a hollow-based .38 Special wadcutter and black powder.
The one (a "no-name" Martini .360) I messed with worked quite well in spite of a fairly rough bore when I carefully "tempered" the nose and bearing body of the bullets and left the hollow bases soft so they could expand and fill the bore.
