Sporter normally refers to the stock mate. you either get a sporter or a thumbhole.
K is for carbine, shorter length version and the 'normal' or full length version is, well, longer! by a few inches. and you get more shots
so a hw100s is a full length with a sporter stock
a hw100ks is a carbine length in a sporter stock
a hw100t is thumbhole and full length
a hw100kt is the carbine in a thumbhole stock.
then theres the FSB in both full length and carbine length with both stock options. e.g. hw100fsbkt or hw100fsbs (fully shrouded barrel) what a mouthful saying all that lol..