There is more to it than barrel length. Gun Powder comes in various forms and compositions. I have had loads using fast burn powder yield greater velocity from short barrels than long and the reverse.
My friends 9MM Glock (poly barrel) and my 9MM M&P (conventional barrel) yield within 10 FPS or so of each other at 1100 FPS range. The glock may be faster today and slower tomorrow.
If you try to fit things into simple rigid catagories you will be wrong 50% of the time.