Brownells - Jack Rowe, Master Gunsmith Series, Bore Size and Proofing, Part 1 of 6

[@ValMartinIreland]

The bore gauge should have a ferule at 9 inches from the head to slide into place in the chamber. This keeps the gauge in line (in line with the bore axis, ) and the head at 90 degrees to the bore to give an exact reading. The difference is minor, but is best practice.

[@patrickc1508]

How does the shotgun bore enlarge so much? Erosion from firing and cleaning, or stretching from the pressure? Also, about how many rounds does it generally take until it gets like that. I’m sure that if it’s by stretching it will greatly depend on the thickness of the barrel walls. If it’s erosion, barrel thickness wouldn’t matter as to the bore enlarging. Only the hardness of the steel and the type of load that you use. I’m sure that steel shot would be worse than lead, as would shooting larger shot than smaller. Like a steel goose load with larger shot vs 7.5’s.

[@dchil15]

Very often barrels will develop pitting inside for many reasons. In order to remove this pitting people will hone out the inside of the barrels. For the most part shotgun ammo will not create significant erosion within steel barrels, even with steel shot. Do your own research as I am not an expert.

[@mohamedelhassani4709]

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