.223 Wylde chamber

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Diagram of an AR type rifle showing the location of the chamber

A .223 Wylde chamber is used on .223 caliber rifle barrels to allow them to safely fire either .223 Remington or 5.56x45mm NATO ammunition.

History and rationale[edit]

In 1957 during research into development of a military .22 caliber rifle the Remington .222 Special was created. Due to there being several .222 caliber cartridges under development, the .222 Special was renamed to .223 Remington. The cartridge became the standard for the US Army in 1962 as the M193 Cartridge.[1]

In 1972 Fabrique Nationale (FN) created a new class of ammunition for NATO. It was based on the .223 Remington cartridge which was being used by the US Army that had greater range and effectiveness. The first iteration of this ammunition was type designated SS109.[2]

Due to differences in the chamber dimensions between the .223 Rem and 5.56 x 45mm NATO (SS109, M-855), the two cannot be used interchangeably, however .223 Remington can safely be fired from firearms chambered for 5.56 mm NATO.[1] As most rifle makers moved to support the 5.56mm NATO specification the reduced accuracy was considered a problem.[3]

Chamber dimensions[edit]

Bill Wylde of Greenup, Illinois compared the two cartridges and changed the chamber of the rifle's barrel to a specification which is called 223 Wylde chamber or 22 Wylde chamber. The chamber is made with the external dimensions and lead angle as found in the military 5.56×45mm NATO cartridge and the 0.2240 inch free bore diameter as found in the civilian SAAMI .223 Remington cartridge.[4] Rifles with a .223 Wylde chamber will typically accept both .223 Remington and 5.56×45mm NATO ammunition.[4] Note that while the .223 Remington and 5.56×45mm NATO chambers have slightly different dimension, the cartridges themselves are identical in dimension.[4] The chamber dimension differences are often confused with the cartridge dimensions and so it is often erroneously thought that the cartridges have different dimensions. The cartridges are loaded to different pressure levels (with the 5.56 being greater), however.[5] (The NATO dimensions offset the higher pressure with a longer throat - often confusing some to think the cartridge itself is longer). This chamber allows the use of both pressure levels safely while also increasing accuracy potential across the range of potential pressures.[3]

Wylde's hybrid chamber was designed to exploit the accuracy advantages of the .223 Remington chambering without problems concerning over pressure or compromising the functional reliability of semi-auto firearms like the AR-15 family when using 5.56×45mm NATO military ammunition.[6] Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the Sport Rifle Competition very well and is one of the preferred chambers for that use.[7] The Wylde chamber is used by rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers.


  1. ^ a b Barnes, Frank C. (19 December 2014). Cartridges of the World: A Complete and Illustrated Reference for Over 1500 Cartridges. Iola, Wisconsin: "F+W Media, Inc.". p. 88. ISBN 978-1-4402-4265-6.
  2. ^ Walter, John (25 March 2006). Rifles of the World. Iola, Wisconsin: Krause Publications. p. 124. ISBN 0-89689-241-7.
  3. ^ a b Sweeney, Patrick (23 February 2010). Gunsmithing - The AR-15. Iola, Wisconsin: Gun Digest Books. pp. 49, 139. ISBN 1-4402-1457-3.
  4. ^ a b c Fitzpatrick, Brad (29 October 2015). "Clearing the Caliber Confusion: .223 Wylde vs. 5.56 NATO". AWC.
  5. ^ McAdams, John (12 May 2014). "The dangers of mixing up 5.56x45mm NATO and .223 Remington rounds". Multi Briefs.
  6. ^ Muramatsu, Kevin (21 November 2014). Gun Digest Guide to Customizing Your AR-15. Iola, Wisconsin: "F+W Media, Inc.". p. 231. ISBN 978-1-4402-4279-3.
  7. ^ Wormley, Stanton (14 August 2014). "The AR-15 for Home Defense: Reliability". American Rifleman.

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