Gas COnsumption
 

How long does one litre of Propane gas usually last for a GBB? A KSC Glock 18c?

2 mags, if you're lucky

depends if you burn through it in full or semi as well
if i recall, my G19 could go about 2.5 mags or so with one fill at 23 degrees or so, while popping shots off at a decent rate
now a LITRE of gas...thats a different story
i would say...quite a while
ive been running 2 or 3 guns off the same can for a good long while now and still have quite a lot left

i get about 25 miles to the gallon

My KJ G23 tends to get about 1000 - 1500 shots/small cylinder of propane, so you should get around that +/-, likely a few more as I tend to fire my mags off quite quickly, cooling the gas a fair bit

I find if you have a WA/TM GBB's there a pain to fill 1 mag maybe....
KWA, KSC are nicer to fill. Also depends on your mags tempeture (cold or hot) while filling and shooting.