Have a look at the sections on early firearms and the transition from bows to firearms in the FAQ. I'm not sure they'll answer all your questions, but the answers there will keep you busy for a while!

Just wondering at what century when guns finally replaced sword/axes/armored knights.

If I may rephrase your question slightly to: "When did swords and body armour stop being issued as standard equipment to front-line soldiers?" then the answer may surprise you. It was about 1915. Here are French cuirassiers marching to the front in 1914 with swords and armour. It didn't take long to catch them up with the realities of 20th Century war, however. By the end of the year, the ones who were still alive had pretty much discarded the armour, and it wasn't much longer until the unit type was basically functioning as infantry.

Swords continued to be issued for a while longer (even into WW2), but they didn't have much function except as a badge of rank, and as a disciplinary tool to goad the stragglers out of the trenches and over the top. Nevertheless, the danger of encountering an officer who had run out of bullets in his pistol and had nothing left but a sword was considered genuine enough that army manuals for bayonet and hand-to-hand combat continued to dispense advice about dealing with sword-wielding enemies right into the 1940s.