How to Calculate Bore Size
- 1). Calculate the weight of the barrel's ammunition from gauge. Divide one pound by the barrel's gauge. For instance, if you're calculating for a 12-gauge shotgun: 1/12 = 0.083 lbs.
- 2). Multiply your answer by 4.664, a figure derived from the density of lead: 0.083 * 4.664 = 0.387
- 3). Find the cube root of your answer. 0.387 ^ (1/3) = 0.728
This answer is the gun's approximate caliber--the bore diameter in inches.