This honestly looks kind of fake. I can't get audio, so I don't know if he explained it away or not, but all I see is targets exploding after getting hit by bullets. That weapon "mounted" is no way big enough to be a cannon, so at the very least it's hilariously staged with pyrotechnics in the targets.

But the inconsistent effects of recoil (there isn't any shift when firing from first person, but you can see it recoiling from the external view), the complete lack of operator safety, and lack of detailed views of the gun from a useful angle leads to me believe that it's all fake.