While perusing a gun shop near my GF's family home a gent walked in and asked for help resolving an issue with his rifle.
Said rifle (Howa 1500 in .223) was not extracting cases and he was having to knock them out with a ram rod.
On inspection the shop owners could not physically remove the moderator from the end of his rifle.
When asked when he had last cleaned the rifle it appeared he never did. The result of this being that the carbon in the moderator had drawn water into it, the barrel and the chamber.
This corroded everything and would require at minimum a chamber polish, 3-4 inches off the end of the barrel, re-crowning, and re-threading of the barrel. Possibly with a trip to the proof house.
So learn the lesson, take your mods off when not in use and clean your guns