The Colorado legislature, still grappling with the definition of "high capacity" has amended the mag limit bill to allow a shotgun to hold up to 28 inches of shotgun shells. This is up from 8, which is up from 5 in earlier versions.
Under this definition, and assuming your shotgun can cycle these things, it is possible for a pump shotgun to hold more rounds than your Personal Defense Weapon* is allowed. Just keep the shell length at or under 1-3/4" and you're good to go.
*(c) Homeland Defense Department.