New to the 870 and shotguns in general. I know that the manual says to open the action halfway to remove the barrel, however, my barrel will come off even if I don't have the action open (it won't go back on though). I know this because I I cleared it, but mistakenly left it closed the first time I went to take it off. It came right off, but wouldn't go back on until I realized I had to open it up. My question- is it normal for the barrel to slide off even if the action isn't opened at all. Thanks.

Yes, but it is not good to do this repeatedly as it can cause stress on the ejector. Always follow the instructions is the manual:)

Thanks. I've had some back luck recently with a new purchase, and I was hoping this wasn't a manufacturing flaw.