That lead ring you mention reminds me of the decades old standard 22 rimfire position shooters have used to indicate a barrel is at the end of its life.For fun 22 shooters need only pull a bore snake through your barrel after every outing.
A couple of points though, some rifles will take about 15 shots to settle in after even a minor cleaning and put shots where the zero is, don't clean it the night before a squirrel hunt you may miss some longer shots.
I've personally never experienced it but have seen pictures of barrel with a lead ring ahead of the chamber that is extremely detrimental to accuracy. Look down your barrel with a scope occasionally if you know someone that has one.
The throat of a new barrel will appear shiny bright all the way around a clock face. As the abrasive glass frit in the primer tends to settle in the bore at its bottom mostly at 6 o'clock, every successive shot adds to it. When about 10,000 rounds are shot, enough frit has roughed up the lands and grooves in the throat that it appears dark from 5 o'clock clockwise to 7 o'clock. Around 20,000 rounds, it's dark from 4 to 8 o'clock. When it's dark from 3 to 9 at 30,000 or so rounds, the bore bottom half is dark for a half inch or more down the barrel.
Shots at 50 yards are going a little off call. At 100 yards, more off call. Time to rebarrel or set it back an inch or more. Then its like a new barrel.
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