I'm kind of confused when it comes to the depiction of space marine helmet variations.

So i'm quite confuse as to the depiction of space marine helmets, as i'm trying to do some research on possibly a drawing, i was looking for the specific type of helmet the emperor's champion uses. However, when I look online, it looks like that other space marine chapters use the same helmet, but I am unsure. Are they the same helmet? Just depicted visually different or there three separate different helmets? For example, I thought that the emperor's champion just used a simple bulwark helmet. However, when I look at the helmet more closely, it looks to be that there are differences. So I am unsure whether this is true or not. It also looks like Sergeant Metaurus,from secret level, uses' a similar helmet to the emperor's champion.

Could any of you guys help me and help explain the differences when it comes to how certain helmets are displayed?