A semiautomatic shotgun, most likely a Saiga 12 gauge.
I could not clearly see if it had a bottom loading mag. It had a pistol grip though. And the barrel was quite long, which identifies not only with a regular hunting shotgun, but also a Saiga.
4th look. It was being held using the pistol grip, but it did NOT have a magazine loader. It most likely is a hunting shotgun with a pistol grip.