You could try Tales from the post war, a post apocalyptic forum game of this style, yes there's guns, you'll just have to have realistic weapons and armor and specify their stats (no need to specify ammo details.), for example you could easily get a sniper rifle in long as you specify the stats, beside, I got a tank gun in (as my character's weapon, I actually have two characters in it.), or maybe Land of Jalaia, where long as your character's balanced it should have a good chance to get in, no tech limits either.