I have a Mossberg 500 Turkey Special, that has become my favorite, for close range work. It has a 20" barrel and has a 3" chammber. I had to install a Simms recoil butt plate, to take some of the bite out of it.
The choke tube that it came with was (doing special) at the .740" restricton. However, it didn't impress me with heavier/larger shot sizes, for coyotes. Therefore, I purchased a Carlson's .680" non-ported and have been very satisfied with the tight patterns it produces...out to 60 yds.
Bowhunter57