The Dardick tround, or simply tround (triangular round), is a unique firearms cartridge developed by inventor David Dardick for use in his open-chamber firearms. Named for its convex triangular shape, the tround allowed the firearm's chamber to be open on one side, removing the requirement for reciprocating motion when chambering and ejecting a cartridge. It was used in several revolvers: the 10-tround Dardick Model 1100, the 11 or 15-tround Model 1500 - and the 20-tround Model 2000. Open-chamber firearm design Dardick (an associate of Melvin M. Johnson) began development of his open-chamber gun in the late 1940s. Dardick's patent 2,847,784, issued in August 1958, is for a pre-stressed open-chamber gun with rotatable cylinder. Essentially this design was a revolver with the exterior of the chambers opened up, forming an open U shape rather than a closed O shape found on typical revolvers. This allowed cartridges to be inserted from the side of the cylinder, rather than from the front or rear, and allowed the cylinder to be rapidly loaded from a magazine. To contain the pressure of firing, an odd number of chambers (typically three) are milled into the cylinder. The cylinder is placed, centered, in a strong frame, so that when ready to fire, the cartridge rests against one side of the frame, and the opposite side of the cylinder rests against the opposite side of the frame. Upon firing, the force is spread to the frame from the cartridge on one side and the cylinder from the other. The pre-stressed part of the design applies to the frame; it is assembled from two parts, which are machined so that the exterior part must be heated, thus expanding, before the interior part can be inserted. Upon cooling, the exterior part contracts, putting the interior frame under compression. This compression counters the pressure put upon the frame by firing. Unlike a traditional firearms cartridge, whose case is roughly cylindrical, the open chamber requires the cartridge to be otherwise. Since the cartridge contacts the frame upon firing, one side of the cartridge must match the curvature of the cylinder's exterior, while the other side of the cartridge must match the half-chamber of the cylinder. Together, the cylinder and frame form the chamber, and the cartridge must not only fit in this space, but also must seal it upon firing, and not deform to prevent cylinder rotation. At this point the rounds