I had no idea either, @HaloJones - google says its one of these: https://www.dixiegunworks.com/index/page/product/product_id/3988/category/335/category_chain/578,349,335/product_name/NA3907+Ted+Cash+Brass+Revolver+Capper
@ironwrx, looks like a clean and simple solution. Made by oneself beats paying on eBay!