I would be shocked if they didn't feed right. the length of shell the gun is marked for is the maximum length, shorter shells will generally work fine. If you go to the extreme end o the spectrum with the aguilla mini-shells you may see feed problems, but 2&1/2 should work well enough.
That being said, there no good reason to use the shorter shells if you dont have to. I bet someone with an older pump or double that cant shoot most modern shells would be willing to do a straight round for round trade for standard 2&3/4" or 3" shells.