6mm BR

The 6mm BR / 6.2x39mm is a centerfire cartridge created for benchrest shooting. The cartridge is also known as the 6mm Bench Rest or simply 6 BR, and has also developed a following among varmint hunters because of its efficiency. There are two basic variants of very similar dimensions, known as the 6mm BR Remington and the 6mm Norma BR.

Soon after the introduction of the .308 Winchester-based wildcat .308×1.5" Barnes cartridge, wildcatters and experimenters began developing their own wildcats based on .308 Winchester. By 1963 there were several .22 (5.56 mm) and .24 (6 mm) caliber cartridges based on the Barnes’ cartridge. The new cartridges’ accuracy and efficiency was noticed by the bench rest shooting community. The .24 caliber (6 mm) cartridge version became known as the 6mm Bench Rest or the 6mm BR due to its widespread use in the sport of bench rest shooting.

Because the cartridge was a wildcat and was not standardized until several years later, several variations of the cartridge existed. Cases required fire forming in the chamber as chambers of the rifles varied from one to another. Several 6mm BR variants exist apart from the Remington and Norma versions: the 6mm BRX, 6mm Dasher, 6 mm BRBS 6 mm UBL and 6mm BR Farè. These wildcats cartridges require reshaping factory cartridge cases and handloading. Over time, some wildcats became standardized and officially listed by the C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) and commercially available as factory produced brass for handloaders.

In 1978 Remington started manufacturing their Remington 40-X rifle in the 6mm BR and named their version of the cartridge the 6mm Bench Rest Remington. By 1988 Remington was also manufacturing ammunition. Remington continues to offer the 6mm BR Remington in the 40-X series rifles. The Remington version of this cartridge is now considered to be obsolete.

In 1996 Norma of Sweden introduced the 6mm BR Norma which was dimensionally similar to the 6mm BR Remington. However, the chamber of the Norma version provided a longer throat making allowances for the seating of very low drag (VLD) bullets. It was designed from the beginning to optimize accuracy, barrel life, and case capacity in a 6 mm cartridge for 300–950 metres (328–1,039 yd) target shooting. As such it couples a sensible case volume (2.47 ml) to bore area (29.52 mm²/0.2952 cm²) ratio with ample space for loading relatively long slender projectiles that can provide good aerodynamic efficiency and external ballistic performance for the projectile diameter. This is the most common variation of the cartridge used today.

The 6mm BR Norma has become a popular chambering in match rifles used in 300 metres (328 yd) ISSF and CISM and other 300 metres rifle disciplines.

In 2025 the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) rulings contained four 6mm BR chambering variants.

Becoming listed by the C.I.P. ends the wildcat status of a cartridge by law in C.I.P. member states.