Can you explain this? I have noticed I get more action with the red circle - and wondered why.
Yes I can. It's all about the resins used.
The measles ball, the red Aramith logo ball and the blue circle are all made with Aramith Super Pro Resin, the same resin used for all of the balls in the sets that each of these cue balls comes with.
The blue Aramith logo ball is made with Aramith Premium Resin, the same resin used for all of the balls in the Aramith premium set it comes with.
The new Aramith Black logo ball and all of the balls in the set it comes with are made with Aramith Super Pro Resin just like the Measles, Red Aramith logo and Blue Circle balls and all of the balls in the sets these balls come with. The difference is while the black logo ball and it's set are made with Super Pro Resin as the others mentioned in this paragraph the black logo and it's set are made with the new Aramith Duramith technology, while the same resin as the others it's process is different high tech reticulation, cross linking and curing technologies newly developed by Aramith which while again the same resin these new techniques result in a "harder ball" which doubles service life, helps it maintain a glossy look and has less friction resulting in leaving fewer burn marks on cloth.
Lastly you have the Red Circle, Black Circle and now discontinued Red Triangle and Black Triangle balls. None of these balls come in any of the sets produced by Aramith. They are made with Super Aramith resin with Carom Finish, the same as balls made by Aramith for 3 cushion. This is why they appear different in appearance, finish look, than the ball sets you may find them in while in your local hall.
ALL of these cue balls are the exact same size diameter and weight new from the factory. So all of the rumors of the Red Circle being lighter or a different size are just that, rumors. I've seen other threads were some here break out their handy micrometers & kitchen scales and offer up that their measurements and weighing and show them to be different, if the balls are new they're not different. Most of the time these theorists are measuring balls that have different service lives prior to weigh in & measurement as when all are new they are all the same.
If you play 3 cushion and pool you'll notice 3 cushion balls seem livelier when playing 3 cushion than pool balls are when you're playing pool, some don't notice it, but they are. Some that do notice attribute it to the livelier rails on a 3 cushion table and the fact that the table is heated, it's not that, it's the balls.
The reason the Red Circle seems livelier when placed with a set of pool balls is the different resin finish between it and the rest of the balls, it's livelier by design and seems even more so because it is just "different" than the material of the rest of the set. This has led to the rumors of it being lighter, it isn't. Also with it being said it's a different size, it isn't, when new. As we all know balls do wear and get smaller and lighter over time and measurements of balls that have been in service for awhile have lent to these rumors.
The Red Circle became popular amongst better players many years ago when Centennials were the primary balls used because you could put so much juice on it or draw it a mile when compared to the what seemed like dog Blue Circle cueballs that came with whatever that set as those balls are made with the same rein and most importantly finish as the rest of the balls in the set. The only pro level player I ever heard say out loud in person that he liked the Blue Circle ball back then was Keith McCready. His stroke was so vicious, even more so than the other pros that he could yank the ball anywhere. This led to many places and players removing the Blue Circle from the Centennial sets replacing them with singularly bought Red Circles and also Pros, Shortstops and Road players carrying a Red Circle with their gear so that no matter where they played or with whatever kind of ball set their cue ball control was the same.
In closing you'll hear many complain about the grab and juice of a Red Circle, generally players of a lower speed that have not developed the cueball control of the level of players mentioned above who favored it, it perplexes them. Seasoned players learn to adjust touch and speed for the given conditions far more quickly than B level and below players. With a seasoned stroke and knack of adjusting ball speed you can do things with a Red Circle that you can't do with any other cueball, slight nuances make a huge difference in how it reacts. I hope this elucidates this for you. All Aramith info courtesy of the education provided to me by my friend Nikko at Saluc over the years.