What are gapless piston rings and how do you get them onto the piston if there is no gap? Well they are 2 rings in one where the lower part also has a gap and is precision-lapped and honed into the upper part.
This design is typically on the 2nd ring grove above the oil control ring where it does wonders for cutting blowby in everything from Cessna light aircraft to F1 racing cars, heavy trucks, and combine harvesters.
Blowby refers to the forced entry of fuel (thus wasted) and carbon into the lubricating oil and crankcase, this is wasted power and torque as well as adding to harmful NOx, PM, and HC emissions.
You can see a graph below of testing a gapless 2nd ring on a dyno test cell in the United States:
