It's a leader ar-12 (Mka 1919 copy) auto loader, the ammo is factory AA target loads. Functions fine with these smooth shells, but some ribbed 12g get the rims ripped off.
I had a thread on this gun, I need to update it, because I would stay away from these, new on the market and untested trash apparently. Shame because the gun is a blast to shoot.
I would say it's definitely the gun. Could be excessive headspace or an issue that gives the appearance of excessive headspace (action not fully locking up, but close enough that it still fires). On your spent hull, I see what appears to be a fairly hefty ejector mark near the "HS" marking - could be an indication of high bolt speed which could mean that the bolt is not locking up properly.
Well the importer is sending a new locking block for the bolt... No idea if this will fix the problem but I'm hoping so. I'm pretty much clueless when it comes to the workings of a gas operated shotgun.