SL8-4 The H&K SL8-4 is a SL8 with standard G36 handguard and double stacked magazine with G36 bolt carrier group. SL8-5 The SL8-5 differs from the SL8-4 only in that it uses the same long rail with ironsights as the SL8-1. SL8-6 This is a black SL8-1 with short sight rail and vented forearm. This is the most popular version of this rifle on the US market. Originally discontinued on July 28, 2010, Heckler & Koch announced August 2nd, 2021 that the rifle would be making a return. SL8-10 A new model with short rail chambered for the .222 Remington cartridge to respect laws that prohibit certain countries' inhabitants from owning weapons in military cartridges. Mostly made for export to Spain, but it is also available in .223 Remington, like previous models, to replace the SL8-4. Other versions SL9SD A semi-automatic rifle, gas-operated bolt with rotary bolt head using 7.62×37mm (.300 Whisper - a subsonic round made by necking up the .221 Remington Fireball case to .308" and using a 240 gr Sierra MatchKing bullet.) The cartridge will fit and feed from all standard 5.56×45mm NATO magazines. The Whisper has effectively the same power and weight as a standard .45 ACP, but the lower calibre greatly increases armor penetration. The SL9SD uses 20 and 30-round magazines, is 1150 mm (O/A length), 270 mm (height), 58 mm (width) and weighs 4.6 kg (with suppressor). HK R8 A modified version of the SL8, known as the R8, is manufactured with a straight-pull bolt action and uses either a 5- or 10-round magazine. These changes were made to allow the rifle to be marketed to sporting shooters in countries with more stringent gun control laws, such as the United Kingdom and Australia. It retains the general appearance of the SL8 though has a similar sight and carrying handle to the G36 rifle, and is available in black or grey. In April 2008, the government of the Australian state of Victoria said that the R8 may be convertible to semi- or fully automatic firing in violation of state law. Heckler & Koch stated that the rifle was built from the ground up as a bolt-action firearm and that any rifle can be converted to full automatic. In March 2009, the Victoria Police Commissioner officially reclassified the HK R8 to "Category D", restricted to police and military users, because it "substantially duplicates a militaristic firearm