The real problem is in the gas system & it's relation to the chamber. It's hard to explain, but the gas system runs bac under the barrel. The gases allow the chamber to remain warm longer than would otherwise be the case. This allows condensation to form in the chamber. People that are even slightly lax in the care of their weapons will find that rust forms in their chambers. Sticky at best or even cases stuck in the chamber is the result. I have rescued several of them by disassembly of the rifle, removal of the barrel and cleaning the chamber. Cleaning consisted of a drill, 20ga bore brush, small length of cleaning rod and Clover valve grinding compound. It's a one time, maybe 2 time fix as you are slightly increasing the chamber diameter when you remove the rust & slight pitting. It's not perfect afterwards, but it does work & doesn't affect headspace. Main thing is to keep the chamber clean & lubed when in storage.