Any good/bad on dry firing my M&P 10? I know on pistols it takes around 500 rounds or more to smooth out. My trigger is not that bad but it's also not that good. I was wondering if just dry firing it would smooth it out some before I bought a new trigger set up and would it cause any harm.

let'r rip, tat'r chip

Remove your Fire Control Group, clean and grease the sears, pins and the bottom curve of the hammer. This will help smooth out the pull. If you want to know how to re-install the FCG, check this thread. You might have to also remove the right hand bolt release to get the hammer back in-
Installing an AR Fire Control Group (Trigger & Hammer)

Grease it up and dry fire your rifle. Not only will this help break in your trigger, it's good practice