Thanks to reader David, we have several photos of a Sjogren 12ga shotgun. The Sjogren was a very early Swedish semiauto design using a recoil action with a fixed barrel. Most recoil orated firearms function by having the barrel reciprocate backwards when fired, but the Sjogren system is different. It has a locking block connected to the firing pin, which keeps the bolt assembly locked in place as long as the firing pin is in the forward (fired) position. Then a shell is discharged, the recoil energy must first push the firing pin backwards against its spring. This recocks the firing pin and also unlocks the barrel. By this time chamber pressure has dropped to a safe level, and the remaining recoil force can push the bolt back to eject the fired case and load a fresh one.
This Sjogren system was marketed commercially as a 12 gauge shotgun which was somewhat successful and also as a military .30 caliber rifle. The Sjogren military rifle was tested by the British Army at Bisley, but was rejected (the test rifle today resides in the British Pattern Room collection).
We have a period article on the Sjogren system available on the Sjogren Rifle & Shotgun page in the Vault.You can also see the photos provided by David here: