advised to raise his revolver vertically while cocking back the hammer so as to allow the fragments of the spent percussion cap to fall out safely. Otherwise, the fragments could fall into the revolver's mechanism and jam it. Caplock revolvers were vulnerable to "chain fires", wherein hot gas from a shot ignited the powder in the other chambers. This could be prevented by sealing the chambers with cotton, wax, or grease. Chain fire led to the shots hitting the shooters hand, which is one of the main reasons why revolver rifles were uncommon. By the time metallic cartridges became common, more effective mechanisms for a repeating rifle, such as lever-action, had been developed. Loading a cylinder in this manner was a slow and awkward process and generally could not be done in the midst of battle. Some soldiers solved this by carrying multiple revolvers in the field. Another solution was to use a revolver with a detachable cylinder design. These revolvers allowed the shooter to quickly remove a cylinder and replace it with a full one. Fixed cylinder designs In many of the first generation of cartridge revolvers (especially those that were converted after manufacture), the base pin on which the cylinder revolved was removed, and the cylinder taken from the revolver for loading. Most revolvers using this method of loading are single-action revolvers, although Iver Johnson produced double-action models with removable cylinders. The removable-cylinder design is employed in some modern "micro-revolvers" (usually chambered in .22 rimfire), in order to simplify their design. These weapons are small enough to fit in the palm of the hand. Later single-action revolver models with a fixed cylinder used a loading gate at the rear of the cylinder that allowed insertion of one cartridge at a time for loading, while a rod under the barrel could be pressed rearward to eject the fired case. The loading gate on the original Colt designs (and on nearly all single-action revolvers since, such as the famous Colt Single Action Army) is on the right side, which was done to facilitate loading while on horseback; with the revolver held in the left hand with the reins of the horse, the cartridges can be ejected and loaded with the right hand. Because the cylinders in these types of revolvers are firmly attached at the front and rear of the frame, and the frame is typically full thickness all the