I don't institute house rules unless there's a major game balance issue. They're like nukes, to me. I don't use them unless I really, really, need to. And if I really, really, need to, I don't care so much about "making sense," because I can cook up whatever crazy fluff I need to to make a square peg fit a round hole -- what my primary concern is, if a game issue has gotten so bad that I'm considering a house rule, is fixing the problem.
So my intent is to make them (a) less appealing as the automatic, go-to, ammo for Hold-Outs and Light Pistols, (b) keep them a viable option for Mundanes tackling Spirits, because they're one of the few ways they can even make the attempt, and (c) keep the anti-electrical defenses (armor mods) just because if I'm even contemplating a house rule it's because SnS is crazy out of control and I'd rather underpower, than overpower, them.
So, yeah. My quick and ugly and admittedly imperfect suggestion -- that's not, please remember, my actual serious proposal to the SnS issue, game-wide -- is very simple, and doesn't necessarily make sense, but what it does is (in my opinion) keep SnS there as a specialized ammo type that can still give mundanes a shot against spirits, puts them roughly on-par with gel rounds as a nonlethal ammo option in most cases, but allows player characters and well equipped NPCs to be ready for the latter application by still protecting themselves.
Y'all don't have to like it. Hell, even Darrian and his buddies -- an old gaming group of mine -- don't have to. I'm just tossing ideas out there that will fix what I perceive as the SnS issues with a minimum of muss and fuss.
If you've got a better suggestion, I'm sure the forum is all ears.