pistols and revolvers. The handgun model must be readily available, and modifications are not permitted as a rule of thumb. The maximum barrel length is , the maximum sight radius is , and the maximum weight is . The overall length of the firearm can be no more than for pistols and for revolvers. Only open iron sights are permitted, and diopter sights are thus not permitted. The rulebook also further specifies any permitted modifications as well as accepted grip shapes. The shooting position is freestyle, and most opt to shoot lying. An example of a popular handguns for IMSSU Unlimited is the Thompson/Center Contender, as well as production bolt action pistols such as Loppo and Jalonen. IMSSU Standing Same technical rules as IMSSU Production. The only difference to IMSSU Production is that the class is shot from the standing position. IMSSU Revolver Only revolvers. Otherwise the class follows the same technical rules as IMSSU Production. The shooting position is freestyle, and most opt to shoot lying. Examples of popular revolvers include Ruger Single Six and Ruger Super Blackhawk, as well as models from Freedom Arms and Smith & Wesson. IMSSU also has smallbore variations of the fullbore classes which follow the same rules, except that the only cartridges permitted are .22 Short, .22 Long, or .22 Long Rifle, that the target distances are halved, and that diopter sights are permitted in standing smallbore. U.S. national handgun categories As of 2020 most competitions in the U.S. are shot under NRA or IHMSA competition rules instead of using the international IMSSU rules, except for World Championships which are held according to IMSSU rules. The NRA rules lies closer to IMSSU, since NRA is the U.S. representative of IMSSU through the United States Metallic Silhouette Association (USMSA). The National Rifle Association of America (NRA) has a total of 7 categories, which can be divided into 3 Conventional categories and 4 Unlimited categories. IHMSA has a total of 8 categories, which can be divided into 3 Production categories and 5 Unlimited categories. The NRA Conventional and IHMSA Production categories are very similar, and the same can be said for the NRA Unlimited and IHMSA Unlimited categories. There are some minor differences and overlaps between the different three different competition rulesets, with the most important outlined below. NRA Conventional Pistol and IHMSA Production classes In the NRA Conventional and IHMSA Production the handgun must