My old Mossberg 500 field is getting very worn in the action. It's not ejecting spent shells anymore, making it a single shot. Really, I have to push the shell out of the chamber after each and every shot with a long stick!
Anyways, I'd like to buy a Mossberg Mariner 9 shot with the 20" barrell. Could I interchange my old 500 Field barrel and mag. tube (which is in very good condition) onto the Mariner's action and visa versa?

I have one of those, basically a shortened home defense item which now has a longer barrel and the usual plastic stock. If the round doesn't eject (for a pump) you have a "catch" problem in that the hook is not gripping the rim. Likely a matter of spring engagement of the "hook" but as well a worn hook (extractor). Think of it as a spring loaded fish hook which isn't engaging.

There might be a minor issue of chamber condition and the type of rounds you are using. Don't worry too much about the rod. Be hunble. I had to do the same with a stainless 20 ga. survival gun which I should check further so I can at least get some serious shooting and less "stoking" done..

Hallo Arctic gun
I had the same question about the barrels and i searched the web high and low.Some people said ye,some said no.i went ahead and mailed mossberg,they came back to me and said no.After talking to my gunsmith,he said that i should buy the barrel and magazine from a used moss 500 and he would see if it could infact interchange with the 590 Mariner.
Guess what! they do interchange according to my gunsmith.He said that the only thing he had to do was to heat the solder that holds the thread of the mag tube .
I went ahead and sent the barrel and mag to South Africa so I guess I will Have to find out in 20 days if it indeed works.Best of luck .I think the Mossberg 590 is a great buy.
Regards
Johan