Firearms carry a specific theft cap
Most forms limit firearms theft to a stated amount, commonly a couple of thousand dollars, regardless of how large your contents limit is. A collection, or even two or three quality rifles, exceeds that readily, and the cap applies to theft specifically rather than to all losses.
Sporting equipment is frequently capped too
Bicycles, golf clubs, archery and camping gear can sit under their own limits on some forms. A household that camps, rides and shoots can have several thousand dollars of equipment covered at a fraction of its value without anything looking wrong on the declarations page.
Scheduling removes the cap and the deductible
Listing items individually with values gives agreed value cover, usually against loss as well as theft, and frequently with no deductible. For firearms in particular it is the only way to insure a collection properly.