Hum, I like 870's and have quite a few. To answere your question , I bought a special field 12, quite a few years ago. It has a 21" tube. I like it an have used it on quite a number of turkey . It kills well, but I do feel it is easier to miss a gobbler with it than my longer barreled shotguns.. It has no special sights as I use it for quail and grouse.. That might eliminate that problem!
