You could always just do the spaghetti trick. Yank the gas block, put spaghetti into the gas port and break it off flush with the outside diameter of the barrel. Put the gas block back on, turn the barrel over port-side-down and move the gas block until the spaghetti falls into the gas block...tweak until it can fall in an out freely as you rotate the barrel port side up and port side down. From there, you can either mark the gas block location with a stripe of pencil/marker...move the gas block, dump the sketty...return the block to the marked location and tighten.....orrrrrrr just carefully push a cleaning rod down the bore to break the spaghetti...then back up and push the rest of it out as it falls down. If doing the second way, just capture all the pieces so you're sure you didn't leave anything in the gun. https://hbindustries.net/store/shop/ar15-gas-block-aligner-5-56mm/
these work too if you don't like spaghetti.
I just bought one of the Teslong scopes from Amazon. I should receive it on Monday. This online review is what convinced me to buy the Teslong: https://www.youtube.com/watch?v=jsVSVeK-itw
I have a Lyman bore scope....not bad, not the greatest.....I set the gas blocks with no gas tube in place, and put a small light in the gas block, where the gas tube goes...the extra light allows me to see the gas block setting well. Works for me.
I just received and hooked up one of the Teslong scopes. $49.99 delivered / Amazon. I am very pleased with the image focus and overall quality. And I used to own an expensive Hawkeye borescope, so I am not easily impressed. This image has not been post-processed.
Notes:
No software is included, but I have a couple of camera programs on my laptop PC that seem to work flawlessly.
Unlike my other two fibercams (~$25 each), the focus on the Teslong is very close - and adjustable - which works for barrels, and for barrels of different calibers.
I easily fits, with the 45degree mirror, down a .224 bore. I haven't tried yet, but it will probably fit down a 22 rimfire.
I've been watching this thread and haven't seen any activity of late. So, has anyone have any luck or wish to add anything more before I put the trigger?