Do you mean the "snout" on a helmet like this?

You'll likely get more answers on another subreddit like /r/medieval or such,

But, if that's the type of helmet you're asking about, the "beak" is on the visor. Specifically, that style is (now-days) called a "pig-faced" or a "hounskull" visor on a bascinet, and was popular right around the year 1400. The "beak" was developed and protruded like that to act as a glancing surface against blows coming toward the face, specifically from lances while on horseback.