If a dent it properly removed it is very hard to see, next to impossible at times. As long as the barrel wall thickness has not been compromised, a dent is rarely an issue. Bulges are a very different matter, they are hard to remove and they have changed the characteristics of the metal once it has stretched beyond its elastic limit. If you can not see these issues with your naked eye, a bore micrometer helps a bunch. So does a bore scope, but they are usually quite expensive.

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