Mike;
You are of course correct the Crown/G denotes a solid projectile. The G in this case I believe is for Geschoss which loosely interprets to Bullet & not Gewehr for rifle. As the G is most often found on rifle barrels I tend to forget its exact meaning, thanks for the correction.
Hal;
The in-between gauges are set halfway between gauges, given to three decimal places with succeeding digits dropped, not rounded. The gauge sizes them selves are derived from a formula based on the weight of lead & are rounded to three decimal places. thus a 13 gauge is .710", a 12 gauge .729". .729" + .710" / 2 = 1.439/2 =.7195. A bore marked 13/1 thus will accept a plug gage of .719" diameter to the specified distance but not a .729" one. Its exact size could be anywhere between those limits.
In sizes 10ga to 4ga there were two in-between sizes which were marked as for instance 8/1 & 8/2. In this case each size was 1/3 of the space between the two gauges. The actual number then will vary according to the difference in size between two gauges.
