The barrel shank threads are completely different on the two actions. The M1885 barrel also has to be thick enough at the breech to fit the Ruger action properly.
Using that barrel on the RUGER #3 would require cutting off the old shank, re-threading to fit the #3 action, re-chambering, and fitting for the new extractor.
The end result requires a qualified gunsmith and produces a two inch shorter barrel.