try putting the nipples in a container with common paint thinner and let them soak whilst you clean. For reasons i do not understand the cap and powder fouling wipes off and my stainless nipples look like new.The nipple threads in the cylinder will not get very dirty because the nipple is in there during shooting the gun. When you clean the cylinder you remove the nipples toss them with the cylinder into a container of warm water that has a few drops of dish washing soap in it and let soak for a few minutes. Then wash/scrub the parts with a nylon brush and rag/paper towel. I run a .22 caliber cleaning brush (bronze or nylon) into the cylinder nipple holes. I then rinse the parts, dry, oil, put a dab of anti-seize on the nipple threads and install the nipples "snug" and done with the assembled cylinder. I then finish up with the rest of the revolver. I then put it away.