I probably have killed over 300 wabbits with my gun. One ranch I hunt on we have to manage the cotton tail population or they will overpopulate and die off and we will go a few years before they come back. So we decided to start a management program which honestly everyone loves. Its a lot of fun
With a Mil-Dot Berska CQB 3-9x40 I can hit 100 yard bullseye's and I have a dot for 100yds, 50yds and 25yds that are accurate enough for head shots. In order to achieve this I zero the gun at 50 yards. However I did a lot of ammo testing with the gun. I found the only ammo accurate out to 100 yards is Aguila Interceptor. Nothing else even comes close but each gun can be different so I would suggest learning your optic and your ammo.
Now as for hunting the wabbits if your just trying to hit them thats one thing but if you want a clean humane kill or you want to eat the tasty little buggers then head shots are critical. At our ranch the person who puts the most rounds into one rabbit to put him down cleans the whole lot. I promise you this makes people very very accurate or they pass on shots they COULD hit and only take shots they will hit.