If you need to know why not speak to your nearest RA unit or phone up the RSA. All the info should be in aide memoirs and available to your unit anyway. Have you asked your Regimental Training Officer?
Hopefully no-one here will be stupid enough to give you the information you require. Considering the weapon system you are asking about is currently in use on operations.
Point 1 - probably not the sort of info that should banded around on the interweb.
Point 2 - do you really mean the L118? or are you talking about the ammunition used with it? because last time I looked the Light Gun was pretty safe until you added charge and shell.....short of dropping it on your foot, or banging your head on the muzzle brake (no comments please it still hurts)
Point 3 - if you do mean the ammunition and someone felt the urge to risk being ripped to shreds for posting the data on the forum, then an idea of which shell type, fuze type/setting, target type would be useful otherwise it's a lot of variables to play with.
p.s. Am I being a bit too sarcastic or was it just enough?
Everyone except an unfortunate FOO in Canada, 1991. First time I've ever seen someones webbing on fire.........................whilst they were wearing it. Still he'll never have a problem with constipation again.