I did that and it works, but I want a longer focal distance.I just take the side view mirror off my Teslong for a straight ahead view.
Oh, I agree. Machining marks like these should have virtually zero effect on accuracy. I'm actually kinda impressed at the condition of the bore for a 30 year old rifle from an estate sale. A good borescope is a darn handy tool.Those lines are just milling marks, you can see they are all evenly spaced. you see all kinds of things in a barrel with one of these scopes. Those old Gustomsky barrels are not the best, the one in the picture has a tight spot about mid bore.
I have a Bill Large barrel that is just about a one hole shooter at 50 yrds, the scope showed a lot of pitting but it sure doesn't hurt the accuracy. With a bore light the bore looks like a shiny mirror.
I have used mine to check for behind the wall wiring when I was doing a project in the house.I think we have the same scope. It's fantastic but the app wouldn't work for my tablet. I had to get the generic one that the manual calls out. I highly recommend the teslong & it goes to the breech of my flintlock with length to spare. I think the more expensive models with the screen are a waste of money since it's about the size of a cellphone & the picture is much bigger on a tablet or laptop.
You can use them on other things too. I ran mine down the dryer vent line to find a clog. It would obviously work to scope an engine cylinder too. It has definitely already paid for itself.