FYI, my twin brother took these pictures of the bore of one of his
black powdah cartridge arms using one of those
LED 5.5mm endoscopes that are sold on the traders of the likes of eBay and Amazon. They come with a 5' or longer cable that plugs into the USB port of your computer or laptop. There is a CD included with it, that you need to load, to allow for video or screen capture.
The focal length is a good inch or so and if placed any closer, the image is distorted. However, for best use with firelocks, a white cloth cleaning patch or tuft of cotton ball is put down into the bore, which works well to allow the adjustable lights on the endoscope to brighten the image for best viewing.
I thought it was pretty cool!
I hope this is OK to post here on these forums, as many here seem very interested in their firelocks, original or not, and this is a pretty slick and inexpensive way to check the condition ...