Many of us have read that 12-gauge guns made for 2-3/4" paper shells were chambered to 2-5/8" for a better gas seal/transition of wads from shell to bore. And of course we're aware of Sherman Bell's testing of 2-3/4" shells in short chambers. OK, check out this 1904 advert. The new 12 ga Marlin is chambered for 2-5/8" and 2-3/4" shells. Great!
So, can we infer that any 12-gauge American guns made for the early 2-5/8" paper shells were chambered to 2-1/2"?
Also, 12-gauge 2-5/8" smokeless shells were made at least into the 40's by Peters and possibly others. And why was that? What guns were they intended for?
Food for thought
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