Are you for real?
They aren't a hit squad practising to eliminate a genuine target. They're a bunch of soldiers messing about because they have time on their hands.
It's a joke, they obviously don't like him and thought it would be funny. The most stupid thing about it is that someone thought it would be a good idea to stick a recording of it on social media.
While I agree it's a stretch. Pracitising to shoot a public figure like Corbyn is a terrible idea, these guys aren't robots following orders daily. They can snap just like any other normal person so it's hardly a good idea to be encouraging them to shoot at politicians. Alongside that its not a great message to send out to the public either is it? All it takes is one right wing nutter to see that video and think "well the army wants him dead! So i'll do it for England!".
I think some people don't actually understand the fragile state of the country right now. It's all just one big joke when the reality is that there are a lot of very angry people.