The lower assembly probably needs a good spraying with Hornady's gun cleaner and solvent, especially if you have a good trigger. Just a small amount of fouling will mess up a good trigger in a heartbeat. Chrome lined bores don't need a lot of maintenance. You would need to know whether your gun shoots better dirty or clean. If it shoots better clean, then clean the bore often. If it shoots better dirty, then wait until your accuracy starts to drop off, then give it a good cleaning. My two AR's like "clean" and my trigger groups really like clean.