Firearms are a very mature technology. I was told that anything patent able has been patented and is over a century old. All the basic principles, locking mechanisms, etc, were patented by 1900. All the operating principles were understood more than a century ago.
Our firearms are still made of steel, use fixed cartridges, primarily brass cartridges, using nitrocellulose based propellant. What has happened since 1900 is refinement, for example, the mechanisms that used greased cartridges and oilers went away so long ago the shooting community no longer remembers them. In debates with skeptics, they have shown they don't understand the principles. But these same skeptics are aware of fluted chambers, which replaced greased cartridges and oilers. Many mechanisms were tried and discarded over the last century. There has been a sort of convergence in semi automatic mechanisms, the vast majority on the market now use the Stoner rotating bolt in a gas mechanism. You just don't see the long recoil or short recoil high power rifle mechanisms that were in the pre WW2 marketplace.
New materials, specifically plastics, have replaced steel and aluminum, but I also consider that a refinement. Manufacturing techniques have gone in cycles. Pre WW2 firearms were wood and machined steel, very expensive and labor intensive to make. The Germans really pioneered stamping technology and many rifles, and pistols, were a combination of easy to make stamped parts. The SIG P220 is an example of a pistol originally designed to be made out of stampings, and yet, technology advanced to the point that computer driven machine tools replaced humans, and I have a SIG P220 which the major components are now machined.
I do believe that optical sights are going to replace irons, we are seeing firearms with irons and optical sights, in time, the irons will go away.
Until someone comes up with something other than nitrocellulose, the basic principles of our firearms are the same as they were in the 1880's.