I heard he has no powers, but he's just enormous.
If so how does he withstand being shot so many times?
The good guys seem to be foolishly aiming at his helmet a lot of the time, but surely there were body shots too?
I recall from the comics he has some magical gem that turned him into this behemoth. He's as strong as the Hulk and invincible.
shareJekporkins is correct. In the comics, at least, Juggernaut (Marko Caine) touched a ruby of Cytorrak which granted him strength equal to, if not greater, than Hulk (at least Hulk at rest. As we all know, the madder Hulk gets, the stronger Hulk gets.) and invulnerability to harm. He was a major foe of the X-men for many years.
I haven't read comics much for many years. I understand he started to lose his powers for a time, but did regain them.