While I'm less of a grognard about it, as I get older - I never cared for Modern, Future, near-Modern, near-Future games. I did play some Traveller and Space Opera, as well as a short campaign with Twilight 2000, back in the 80's just to give them a try - but I didn't really care for it.
And though I'm more open-minded regarding later history, my primary historical interests, let alone gaming interests stops at the Rennaissance. Truth tell, I don't really even care for the Middle Ages, much preferring the Dark Ages (fall of Roman Empire up to the Norman Invasion) and earlier.
So guns? Too modern for my gaming interests.
I'll also agree with others that gun game mechanics, IME, never really worked well with D&D. I'm sure someone could figure out one that did work, but even still - I even cringe thinking of full plate armor as being too modern for my tastes, that's high middle ages too modern for me!
GP