dumb question perhaps, but whats the difference?

One has a jacket and a hollow point the other is a lead or plated bullet that has a hollow point. The words are generic terms describing basic bullet construction.

Typically, the jacketed HP will contain pure or very nearly pure lead and it's the softness of the pure lead that leads to expansion.

Non-jacketed HPs may be of a harder alloy in order to provide accuracy and expansion may or may not accompany this alloy.

A hard alloy HP driven fairly fast will likely tend to break apart rather than expand when it hits.

ward

a bit 'off topic' but use a jewerlry saw on cast slug to form a 'dumdum' slug.
largest bore I've shot thru into a test medium of soaked wet brown paper and phone books is the 9mm Makarov. impressive wound channel. from about 15'