Hi Bob

I shot ten metre running boar (Running rat) quite seriously many years back, Now PC incorrect, and now just moving target, we had the same problem getting scopes generally set for 100 mts correct at 10 mts.

Don't mess about trying to adjust the lens its a real hassle, what we did was go to a local lens maker/optician, you need a +0.1 dioptre lens added to the front, the tolerance on plain lenses is 0.1 of a dioptre, which is what you need, if you have a friendly one he will sort and test his plain lenses until he finds one on 0.1.
Get it ground to the correct diameter, then pop out the front ring put an "o" ring either side of the lens and pop the ring back. Voile, corrected to ten metres, and easy to take out to return scope to standard.

Have Fun
Robin