I'm pretty sure I'm understanding you correctly and you say you can remove and re-install your 28" barrel with no problem, but your two accessory barrels ( turkey barrel and fully rifled deer barrel) are giving you difficulties. They should install exactly the same( and just as easy) as the 28" barrel. You could also try with the slide all the way back. Its not what Mossberg recommends, but I've never had a problem with it. If that doesn't work take it back to where you bought it.
Jim
You understand correctly.
If you can remove and re-install one barrel but not the other two, I'm guessing there is something wrong with those barrels. I'm a little over an hour north of you, if your up for a road trip tommorow morning, bring it up and I'll have a look. I have two more Mossberg 500's to compare it to.
Jim



























