correct. Available for this round are AR-15 upper receivers and M1911 slide assemblies. Many handgun manufacturers have an upper pistol conversion kit to make it shoot .22 LR ammunition. These conversions allow shooters to practice inexpensively while retaining the handling characteristics of their chosen firearms (with reduced recoil and muzzle blast). Additionally, .22 LR cartridge conversion kits allow practice at indoor ranges which prohibit high-power firearms. Owners of guns that use gas systems, such as AR-15 sport style rifles, normally avoid firing non-jacketed .22 LR cartridge ammunition, as the use of unjacketed ammunition may cause lead-fouling of the gas-port inside the barrel and costly gunsmithing procedures. This can usually be mitigated by swapping the conversion kit for the standard bolt carrier group, and firing several full-powered rounds to clear the gas port and tube of any accumulated lead fouling. While not 100% effective, the extremely hot incandescent gasses produced by centerfire rifle ammunition will help to clear any lead fouling from the .22 LR ammunition. A wide variety of .22 LR ammunition is available commercially, and the available ammunition varies widely both in price and performance. Bullet weights among commercially available ammunition range from , and velocities vary from . .22 LR is the least costly cartridge ammunition available. Promotional loads for plinking can be purchased in bulk for significantly less cost than precision target rounds. The low cost of ammunition has a substantial effect on the popularity of the .22 LR. For this reason, rimfire cartridges are commonly used for target practice. .22 LR cartridges are commonly packaged in boxes of 50 or 100 rounds, and are often sold by the 'brick', a carton containing either 10 boxes of 50 rounds or loose cartridges totaling 500 rounds, or the 'case' containing 10 bricks totaling 5,000 rounds. Annual production is estimated by some at 2–2.5 billion rounds. The NSSF estimates that a large percentage of the US production of 10 billion cartridges is composed of .22 LR. Despite the high production figures there have occasionally been shortages of .22 LR cartridge in the contiguous United States, most notably during the U.S. ammunition shortage of the late 2000s and early 2010s. Performance The .22 LR is effective to , though practical ranges tend to be less. After 150 yd, the ballistics of the round are such that it will be difficult to compensate for the large "drop". The relatively short effective