Something to think about regarding springs. I recently bought a new, older stock, K40. Its had about 600 rounds through it since I bought it. It always had a little hesitation when going back into battery. Just a tiny little nudge was needed, every once in awhile, to get it to close completely.
So, I ordered a couple new recoil springs and guide rods.
Top is the spring I took out of the gun. Same number of coils, but, markedly shorter. I don't know if it took a set from sitting on a dealers shelf for years, or from the rounds I have put through it. They may have even changed the spring style for all I know.
The gun goes into battery very smarly now. I haven't shot it much since the spring change, but, I'll take it out and look at it after a few hundred rounds and post back.
Obviously, that much change in the length of the spring made quite a difference in its return energy. I'm a believer in changing out something as cheap as a recoil spring on a regular basis. Especially now.