Best way to trim dado rail

[swampydrill]

I'm in process of decorating hall stairs and landing, i am going to change the architrave and skirting boards but plan on leaving the dado rail, the issue is that the old architrave is the old bullnose type, the newer type is slightly wider and so i have to trim the dado rail back slightly, what is the best thing to use?

 

[gregers]

hand saw

 

[big-all]

if your talking say 2mm then just reduce the setback at the front
use a hand saw as said or a bosch 180e
or if you have a gouge and not to many to do recess into the architraves