Based on the M16 assault rifle, the SR25 instead uses 7.62mm caliber rounds. It uses a 20-round magazine. It is a semi-automatic sniper rifle that is frequently used with a sound suppressor.
The SR-25 is a rifle in use by the USMC (U.S. Marines), US Navy SEALs and Australian Special Forces. It was developed by Eugene Stoner and Reed Knight (The designers of the AR-15/M16 series, on which the SR-25 is based on) in the 1990s. During the early 1990s, it was adopted by the SEALs as the Mark 11 Mod 0 and later, was adopted by the Marines. The Australian SAS-R also makes use of the SR-25 as a recon rifle. An updated version of the SR-25 won the 2005 US Army Semi-Automatic Sniper System (M110 SASS) competition and is currently in use by the U.S Army and Marines. The SR-25 is capable of being used with a supressor.
The SR-25 shares the same basic action of the AR-15/M16 platform. It uses a gas-operated system with direct-impingement gas drive. However, instead of a gas piston, powder gases are fed from the barrel and through a stainless-steel tube back into the receiver, and then into the cavity inside the bolt carrier through the gas key. Inside the bolt carrier, powder gases push it back against the bolt, thus first causing the bolt to rotate and unlock from the barrel, and then to cycle the action.