« Reply #4 on: January 20, 2012, 12:56:11 AM »
strangefire,
The given bore sizes are "nominal" not exact measurements. There are manufacturing tolerances the result in bores with varying diameters. When shooting cast lead bullets in rifles one needs to know what bores size a particular rifle is so that the correct bullet OD can be used. For a rifled shotgun barrel I am assuming that the bores also have some variation and if you really want to know your exact bore diameter of a particular barrel you would need to slug the barrel. Slugging a barrel involvements inserting a slightly underbore size piece of soft lead into the barrel and againist an obstruction of some type and then using force to expand this soft lead into the barrel. The slug is then removed and measured to determine the bore size.
BB
Steve's Pages has a spreadsheet with shotgun gage/bore dimensions. From that page;
12 ga. .729" nominal
20 ga. .615" nominal
Since bore dia. tend to very you would need to slug yours to know the exact bore size.
BB
I don't understand by what you mean by "you would need to slug yours to know the exact bore size"
Could you please explane? Thanks
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