Fin2Feather has it right. April 20, 1915 is the patent used for the model 315 Stevens. US patent #1,136,247 issued to G S Lewis, Springfield Mass. The reason for the different pin placement is the 315 is striker fired & the 311 type has internal hammers. The higher rear pin placement on the 315 is for the sear arrangement to release the spring loaded strikers. I once had a 20ga built on this action marked "Central Arms Co". I mentioned it here one time, but didn't recall about the different pin placement or the patent date, only that it was striker fired. The rest is Compliments of "Russ", long may his memory live.
I expect the confusion comes from the fact that Iver Johnson built a "Hercules" model under their own name & quite possibly with other trade names as well. The guns pictured here though are Stevens.
