Pooch, You might be referring to 'rivelling'. There is a thread on this from about a year ago. A rivelled barrel is pretty much a shipwrecked barrel....very few can be remedied, but I guess a few can. A rivelled barrel will not pass proof in the UK unless remedied, which I understand is very hard to do. Cause of rivelling is unknown, but a possibility includes shooting 'boomers' in guns with thin barrel walls. There are other theories as well.

Socialism is almost the worst.