I think Brian is right. I have owned a bought 1/2"bore Compression ignition engine that had no piston rings. - Just 2 grooves, because the gas dynamics resist blow-by. The clearance of piston to bore was incredibly small - which helped get the compression high enough for auto-ignition.
But a model I made, only ran for a couple of minutes, before the clearance was too big to get enough compression. With cylinder head changed to glow-plug type, I got another couple of minutes running before the piston to bore leaked too much so I had no compression.
However: It may be possible to make wire rings = wind a coil onto a shaft and select middle coils, after slitting. Hold coils tight on the shaft while slitting. I have not made any, but that's what the factory does. There is an "end effect" for the tangential load of the ring within about 30 degrees of the split, where the ring, when compressed in the bore, is trying to straighten more at the "ends", so this is compensated by bending-in the coil maybe 1 wire diameter at the ends. Of course, it may not be significant with wire rings in tiny bores? Also, dress ends so there are no sharp edges to score bores. Don't chamfer, just remove burrs and "sharpness" at the cut.
Modern cars have wire rings, not cast iron, (Mostly, as some have Lithium Batteries!).