 22 TCM. It's a bottleneck round with a 40 grain, 22 bullet in there. It's fast, it's loud, it has a huge muzzle flash. Its main competitor is the 5.7 by 28 millimeter arms cord. It's the only producer in Rock Island. It's the only producer of the firearms. Rock Island polymer pistols that chamber it, but that has to be chambered in 22 TCM-R. The R is just a hair shorter 22 TCM-R made it difficult to purchase and everything was based on Rock Island armory. The 5.7 was popular enough to have companies like Ruger, Diamondback, Palmetto, Caltech. This was once a up-and-coming champion has now died off.