technically there is no functioning silencer for airsoft(well in the ways that you want). That silencer will do two things for you.
1: it will reduce the noticible gas expulshin from the barrel
2: it will give you the option to add a longer inner barrel
Umfortunately that silencer is too heavy for your gun. You'll have to get a silencer of 100-150mm in length.if I'm not mistaken(I might be it's been awile since I've seen a g18) the key holes are attached to the slide.
They have a 120mm at airsoftsmith.com. For some reason I can't coppy the URL.
Post a pic once your done
sticks