Have you tried shooting CCI CB ammo? I shoot that into a trap in my basement and its so quiet you don't need ear protection. It won't cycle the action obviously but great for vermin eradication. And you are correct, it is accurate. But when I use CCI CB in my CZ452 with the longer barrel it makes it quieter than my pellet gun.
On a side note, I masked off the barrel/receiver union so that it didnt affect the fitment.
If I can find a few hours today I am going to hit the bolt, firing pin, extractor and knife grip with graphite black.
I'm famous for doing projects 95% and never completing them. I need to finish this one before I get distracted. LOL