Only thing I can tell you is to slug your bore. Get a pure lead ball of 23 calibre and push it through your bore with wooden dowel. Have a soft pillow for the ball to fall out on and then measure the lands and grooves on the ball. That will give your bore size. Keeping in mine that lands and grooves are the opposite in the bore to what is in the ball. Be sure to use pure lead as tinned lead is harder to push.
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