USED- The Remington 550-1 is a classic, American-made semi-automatic rimfire rifle. This one features the 3/8in grooved receiver with a 4x scope included. It has some minor wear and blemishes on the barrel. The bore is very good and in overall great condition. Introduced in 1946 as an upgrade to the base Model 550, it carved out a massive legacy for its unique ability to seamlessly mix and fire different ammunition sizes. Remington manufactured roughly 764,573 units across the 550 series before discontinuing it in 1971. The defining feature of the 550-1 is its floating chamber mechanism (also known as a "power piston"), designed by legendary firearms inventor David "Carbine" Williams. Standard blowback semi-automatic rifles rely on the gas pressure of a fired round to push the bolt back and cycle the action. Because a .22 Short round generates far less energy than a .22 Long Rifle (LR), normal semi-autos will jam if you try to shoot the smaller cartridge. The floating chamber solves this: when firing a tiny .22 Short, the gas forces a small, movable piston inside the chamber backward, acting like a booster to throw the bolt open. When you shoot a .22 LR, the piston locks flush. This allows the rifle to cycle .22 Short, .22 Long, and .22 Long Rifle ammunition interchangeably and automatically from its tubular magazine without any adjustments. Action: Blowback Semi-Automatic Barrel Length: 24 inchesWeight: ~128 oz (approx. 8 lbs) Magazine: Under-barrel tubular magazine Capacity: Roughly 15 rounds of .22 LR or up to 22 rounds of .22 Short Sights: Fixed front dovetail, adjustable rear iron sights; grooved 3/8-inch receiver for scope mounting on later models. Stock: Full-sized American Walnut ISS2486