ok you have the 2 different stock types the sport and the thumb-hole, then there is the variant of full length or carbine so basically 4 different models if you exclude the new shrouded version (which i would )the full length version gives you 10 mags in .22=140 shots, the carbine .177 is 5 mags i think i read somewhere so the others are roughly in between oh and the HW100 IS REGULATED!!! just to put a point in before some goes on about sweet spot and all that ps make sure you get one with a quick fill on the front as its then the mk2 saves unscrewing the bottle everytime hope this helps