Not much to contribute here since the only custom action I've handled is my TL3 (which is awesome), but when I was considering coatings, I talked to a guy at Bighorn and he said he actually coats his with just plain ole' Cerakote, which he smooths on the inside of the action with a flex ball hone. He said nothing wrong with DLC but he likes Cerakote just as well if not better. TL3's have quite a bit more clearance between the bolt body and the action than some of the more traditional custom actions by design, so the extra thickness of Cerakote versus a PVD coating shouldn't make any difference.