Revolvers chambered for the .22 R.F. cartridges, (.22 Magnums in particular) require a heavier mainspring to insure ignition. As the frame and hammer get smaller the heavier spring becomes even more important.
That said, a 16 to 18 pound DA. pull would be excessive. But are you sure that this is really what the pull is, or does it just feel that way?
It is also possible that something is binding a bit, and the heavy pull isn't entirely the fault of the mainspring. Either put that plastic ring back on the cylinder, or EMPTY CASES into the chambers and dry fire the gun several hundred times. This may smooth it out considerably. The lockwork may also be dry and need a few drops (no more!) or oil. If nothing works try a spring for the model 85 and see if it does work, with the expectation that it will not. Doesn't hurt to try though, unless the revolver might be used for self-defense. If that's the case don't fool with the springs.
