Bottling from a Keg

So I have been kegging for several months and now I have a big stout I want to bottle but I want to bottle from my corny. What is the best procedure on doing this?

I realize I will probably need to buy some sort of bottling equipment like blichmann's beer gun. So do I carbonate in the keg first with co2 or do I use priming sugar? I would prefer to use co2 then bottle after I have carbonated in my corny if possible.

I really dont have any idea on the best method so I need help from all the great homebrewers out here.

Thanks

this works great!
https://www.homebrewtalk.com/f35/we-no-need-no-stinking-beer-gun-24678/