Most US 12 guage shotguns before the smokeless era had 2 5/8" chambers, and when they started making smokeless shells for them, they kept that length available for many years (since the shotguns lasted many years).
They are no longer common, for sure, although Shurshots in 2 3/4" are. You need to make sure that a potential buyer knows that they are not the "common" length. If the box is in good shape, somebody will want them.
Was Mike Armstrong. Got logged off; couldn't log back on. RE-registered my old call sign, Mesa.