Welcome to the forum. The Black Diamond is a very good rifle; about as good as they come. It's also a very dirty rifle, especially when used wth .209 primers. The nipples that come with the rifle are the Flame Thrower Nipples with three vent holes. They allow a lot of blowback that really cruds things up.

Put a plain old TC musket cap nipple on my first Black Diamond and it stays a lot cleaner. Just installed a musket nipple for my current Black Diamond. Eventually i want to have a 209 breechplug that eliminates the nipple made for my gun.