Red Circle and Pro Cup Cue ball.
If both balls are the same size and weigh the same, it must be the construction and materials used.
The Pro Cup ball (as read from back of the package details) is constructed using the same process as carom balls.
Unless you have brand new balls and brand new cue balls, measuring weight and diameter will almost always be different.
It has been my experience that most comparisons have been made with old red circle cue balls that are lighter and smaller than the new Pro Cup cue ball.
If you take the striped balls of a set that is 5 playing years old and compare with the same playing age red circle cue ball.. the cue ball will be smaller than the stripped balls. Reason being (IMO) is that the stripes don't get played with as often as the solids (again, IMO, 9 ball being more popular in a pool room than 8 ball)
Exactly Right and the CB will be the smallest since it is hit on every shot unless you're playing English Billiards.
Aramith or better said Saluc is a PRECISION BALL MANUFACTURER. They make balls for critical industrial applications not just pool and billiards. They are THE PREMIER manufacturer for our sports. They would not be there if they couldn't or wouldn't hold size tolerances on all their products.
Chalk is abrasive. Playing on dirty tables is like playing on sand paper. At least as far as the balls are is concerned.