The Bushmaster XM-15 series (or XM15) is a line of AR-15 style semi-automatic rifles and carbines previously manufactured by Bushmaster Firearms International, LLC. Variants include the Bushmaster M4-type Carbine, Patrolman series, QRC series, Bushmaster XM15-E2S, and the Carbon 15 line. Variants The standard XM-15 has a forged 7075T6 aircraft-grade aluminum upper and lower receiver. Barrels of XM-15 firearms have a heavy profile and are hard chrome-lined 4150 alloy steel or 416 stainless steel. In Bushmaster's 2016 sales brochure, all new-production XM-15s are stated to be supplied with a 4150 steel barrel. The standard barrel has rifling of 1 turn in 9". E2S Series: The basic E2S is fitted with a 16-inch carbine-style barrel. E2S Target - 20" heavy-barrel target rifle with A2-style stock and carry handle upper, also available with 24" and 26" barrels. E2S Shorty - 16-inch version with a "shorty" handguard. E2S Shorty AK - Shorty variant with 14.5-inch carbine SBR barrel with an AK-74-style muzzle brake permanently welded to the end to increase the overall length to 16 inches. E2S Dissipator - Variant with a Bushmaster-designed 16-inch "Dissipator" barrel. This mounts a false gas block with a front sight at the 20" position with the real gas block in the carbine position and concealed under a rifle-length 12" handguard. QRC Series: Formerly known as ORC ("optics ready carbine"), but now styled as QRC ("quick response carbine"), are flat-top rifles without iron sights, provided with a simple 1x20 red-dot optic. QRC is chambered in 5.56x45mm with a 1:8 twist melonite coated barrel, M16 style bolt carrier group & mil-spec buffer tube. Patrolman Series: - 7" or 10.5" barrel "pistol" version with a free-float handguard and no stock. Also available as a military or LE select-fire version. Bushmaster M4-Type Carbine Carbon 15 Notoriety The Bushmaster XM15-E2S "M4 type" carbine first gained notoriety for its use in the October 2002 Beltway sniper attacks. A Bushmaster XM-15 was used in the December 2012 Sandy Hook Elementary School shooting. Just before the two-year anniversary of the massacre, nine families of the 26 victims of the shooting filed a class action lawsuit in Connecticut against Bushmaster, Remington Arms and others, seeking "unspecified" damages for the defendants' purported negligent entrustment and illegal marketing of the XM-15 rifle. Plaintiffs argued that both theories of liability fell within exceptions to the 2005 Protection of Lawful Commerce in Arms Act, which affords broad civil immunity to gun