Guns in the middle ages were mainly experimental and had a tendency to jam, blow up, be really inaccurate and required someone to create and mix the gunpowder and someone to find a good source of something to use as ammo. I am actually really against guns in PS, but Peacer poses an interesting topic. So, we would need a flint mine and a source of saltpeter at least. A flint mine might be good if there are eventually campfires in PS, BTW. Also, the earliest cannons in the middle ages were usually made for only one purpose, that being blowing holes in castles. Anything more accurate than than or the shrapnel burst blow at a group of opponents was pretty much out of the question. It took a while to get to the arquebus and blunderbluss flintlock type of guns and I think that by the time those were in use, we would be way out of the time period for PS. But nobody said anything about seige engines... of course we would have to have castles. And, until people actually HAVE to eat, a seige would not really be compelling to the players...