whoa

[Stalker0]

As far as shrink item wasn't intended for offensive purposes....bull!! I can use fireballs for noncombat, and I can use shrink item for combat, I'm a wizard with a 20 + whatever intelligence, I think I can find new ways to use spells

That aside I'd treat the shrink item as the old inflatable raft scenario. It will fill a space until it can't anymore, then it stops getting bigger. Now, the second you make the container bigger it will attempt to fill it some more until it gets to its proper size, but it won't be busting through iron or anything to do it.

So I won't let a shrunken metal piece burst through an iron door lock, I might allow it to pop through a crack in a wood wall, that's rotted.

 

[myradale]

So you can just put a shrunken item into a small container and have the spell duration continue forever?

 

[DaveStebbins]

As I said in the actual thread, I would rule a re-growing item is shunted to a space which will hold it. I referenced spells like dimension door and meld into stone, as well as the older (1E, 2E) versions of things like blink.