The 20 ga. will only shot a maximum of twe thirds the amount of shot in your pattern so the patterns will be less dense. I have and use both and with the 20 gauge I use a size tighter choke and have to be more precise shooting it.
Shooting lead through the bare threads will not damage the gun but it is a real pain to clean the threads.
You should pattern your shotgun at the ranges you typically use it. Dove are small and fast so getting on target fast and follow through is imperative. Check to see if there is someone who "fits" stocks. Having your shotgun fitted to you will not only give you more hits but it will also be more comfortable to shoot.
