6mm BR

The 6mm BR 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.[5] There are two basic variants of very similar dimensions, known as the 6mm BR Remington and the 6mm Norma BR.

6mm BR Remington
6mm BR, 6mm Dasher and .308 Winchester cartridges
TypeRifle
Place of originUnited States
Production history
DesignerWildcats: Various
Commercial: Mike Walker
DesignedWildcats: 1962-1963
Commercial: 1978
Produced1978-present
VariantsSeveral. See article.
Specifications
Parent case.308 Winchester
Case typeRimless, Bottleneck
Bullet diameter.243 in (6.2 mm)
Neck diameter.270 in (6.9 mm)
Shoulder diameter.458 in (11.6 mm)
Base diameter.473 in (12.0 mm)
Case length1.560 in (39.6 mm)
Primer typesmall rifle
Maximum CUP52,000 CUP
6mm Norma BR
TypeRifle
Place of originSweden
Production history
ManufacturerNorma
Produced1996
Specifications
Parent case6mm BR Remington
Case typeSemi-rimmed, Bottleneck
Bullet diameter0.243 in (6.2 mm)
Land diameter0.236 in (6.0 mm)
Neck diameter0.271 in (6.9 mm)
Shoulder diameter0.458 in (11.6 mm)
Base diameter0.469 in (11.9 mm)
Rim diameter0.473 in (12.0 mm)
Rim thickness0.054 in (1.4 mm)
Case length1.560 in (39.6 mm)
Overall length2.440 in (62.0 mm)
Case capacity38-39.5 gr (2.45-2.55 ml)[1]
Ballistic performance
Bullet mass/type Velocity Energy
6.8 g (105 gr) Lapua GB542 Scenar-L (OTM) 815 m/s (2,670 ft/s) 2,258 J (1,665 ft⋅lbf)
6.8 g (105 gr) Lapua Scenar (OTM) 850 m/s (2,800 ft/s) 2,457 J (1,812 ft⋅lbf)
5.8 g (90 gr) Lapua GB543 Scenar-L (OTM) 900 m/s (3,000 ft/s) 2,349 J (1,733 ft⋅lbf)
Test barrel length: 670mm
Source(s): [2][3][4]

Cartridge history

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.[6] Several 6mm BR variants exist apart from the Remington and Norma versions: the 6mm BRX,[7] 6mm Dasher,[8] 6 mm BRBS[9] 6 mm UBL.[10]

6mm BR Remington

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.[11] By 1988 Remington was also manufacturing ammunition.[12] Remington continues to offer the 6mm BR Remington in the 40-X series rifles.[13] The Remington version of this cartridge is now considered to be obsolete.[12]

6mm Norma BR

In 1996 Norma of Sweden introduced the 6mm Norma BR which was dimensionally similar to the 6mm BR Remington.[14] However the chamber of the Norma version provided a longer throat making allowances for the seating of very low drag (VLD) bullets.[12] It was designed from the beginning to optimize accuracy, barrel life, and case capacity in a 6 mm cartridge for 300–600 metres (328–656 yd) target shooting. As such it couples a sensible case volume (2.45 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.[14] This is the most common variation of the cartridge used today.[15]

The 6mm Norma BR has become a popular chambering in match rifles used in 300 metres (328 yd) ISSF and CISM and other 300 metres rifle disciplines.[16][17]

Design

The 6mm BR Remington cartridge is a .308×1.5" Barnes cartridge necked down to accommodate .243 bullets. The .308×1.5" Barnes cartridge is based on the .308 Winchester case shortened to 1.5 inches (38 mm). It is one of the earlier cartridges to follow the short, fat design concept. Short fat cartridges have characteristics that make them more efficient and accurate.[18]

6mm Norma BR

The 6mm Norma BR cartridge was introduced by Norma in 1996. It is based on the 6mm BR Remington cartridge, although where Remington's cartridge was intended for bullets of about 70 grains (4.5 g), Norma standardized their set of chambering specifications for a very low drag (VLD) bullet of over 100 grains (6.5 g), thus realizing the long-range capabilities of the cartridge. This required a much longer throat in rifles chambered for the Norma cartridge.[19]

See also

References
  1. 6mmBR Cartridge Guide
  2. 6 MM B.R. NORMA / 6.8 G (105 GR) SCENAR-L PRODUCT
  3. 6 MM B.R. NORMA / 6.8 G (105 GR) SCENAR PRODUCT
  4. 6 MM B.R. NORMA / 5.8 G (90 GR) SCENAR-L PRODUCT
  5. Simpson, Layne (2005). Layne Simpson's Shooter's Handbook: 600 Questions Answered. Krause Publications. pp. 192–193. ISBN 978-0-87349-939-2. The same cartridge in the short action Remington Model 700 rifle and Model Seven carbine would be excellent outfits for varmint shooting
  6. "6mmBR Cartridge Guide". 6mmbr.com. 6mmBR.com. Archived from the original on 24 August 2010. Retrieved 25 September 2010.
  7. Whitley, Robert (31 July 2010). "The 6mm BRX — Myth-Busting with Bob Crone". accurateshooter.com. Accurate Shooter. Archived from the original on 2010-08-10. Retrieved 25 September 2010.
  8. "6mm Dasher". 6mmhot.com. 6mmhot.com. Retrieved 22 September 2010.
  9. "6BR Improved Cartridge Guide". 6mmbr.com. 6mmBR.com. Archived from the original on 15 September 2010. Retrieved 25 September 2010.
  10. "Taming a New Wildcat -- 6 UBL Drives 107s to 3005 fps". 6mmbr.com. 6mmBR.com. Archived from the original on 15 September 2010. Retrieved 25 September 2010.
  11. Hawks, Chuck (2005). "The 6mm BR Remington". chuckhawks.com. chuckhawks.com. Retrieved 25 September 2010.
  12. "6mm Norma BR and 6mm BR Remington". ammo-one.com. Ammo-One. Archived from the original on 27 August 2010. Retrieved 25 September 2010.
  13. "40-X Series". remingtoncustom.com. Remington Arms Company Inc. 2010. Archived from the original on 27 September 2010. Retrieved 25 September 2010.
  14. C.I.P. TDCC datasheet 6mm Norma BR
  15. "6mmBR Frequently Asked Questions (FAQ)". 6mmbr.com. 6mmBR.com. Archived from the original on 24 August 2010. Retrieved 25 September 2010.
  16. "Lapua Sport Shooting cartridges - the 6mm Norma BR". Archived from the original on 2010-12-04. Retrieved 2010-10-19.
  17. 6mm Norma BR DL match cartridge for 300 m rifle shooting product page
  18. De Haas, Frank; Wayne Van Zwoll (2003). "Short Stature, Long Range". Bolt Action Rifles - 4th Edition. Krause Publications. pp. 636–643. ISBN 978-0-87349-660-5.
  19. Barnes, Frank C. (2000). M.L. McPherson (ed.). Cartridges of the World (9th ed.). Iola, Wisconsin: Krause Publications. pp. 2p. ISBN 0-87341-909-X.
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