Ok I know it's ok to leave AR mags loaded indefinatly.  But is it ok to leave a shotgun loaded all the time?  Don't ask me where but on some advertisement somewhere I read you shouldn't leave a shotgun loaded for more than a month because it was bad for the spring.  Of course they where selling springs.  Just curious.

My Mossberg has sat fully loaded for a year now and I have never had any problems with it

I have heard of, but not seen, LE shotguns that the spring has bound inside the mage tube due to rust.  Being that its compressed when it rusts, the theory goes that it rusts to itself and cannot re-expand.  Don't know if there's any valididty to it, but if you were concerned you could always remove the spring every so often and oil it up.

Personally, I would also clean out and oil the inside of the mag tube, especially on a used gun.

I've kept my 870 with extended magazine fully loaded for months at a time over the 10 years that I've had it.  

It still has that original extended magazine spring and works just fine.

Chris

The actual working (loading and unloading) of the spring is what causes it to weaken. Not keeping it compressed or relaxed.