I tried a cheap 5mm USB endoscope camera years ago and couldn't get the results I wanted. I made my own 90 degree mirror but didn't have enough barrel diameter in a .22 rifle to attach the mirror sufficiently. It worked poorly for larger barrels but I really wanted it for .22 so I gave up on it. Here is a 3 year old video I made:
This looks good, especially the 90 degree mirror which is crucial to check rifling condition, I may give a try. Is this the model you bought? Have you fully inserted it into a .22 rimfire barrel with the mirror attached?
https://www.amazon.com/Anykit-Bores...ustrial&sprefix=anykit,industrial,202&sr=1-19