Performance Improvement Experiments With Non C.I.P. Conform Cartridges
Improvement beyond this standard while still using standard .338 Lapua Magnum brass is possible, but the bullets have to be very long (over 5.5 calibers in length) and the normal cartridge overall length of 93.5 mm has to be exceeded making such cartridges wildcats. The common 254 mm (1:10 inch) rifling twist rate also has to be tightened to stabilize very long projectiles. Such commercially non-existent cartridges are termed "wildcats". The use of a wildcat .338 Lapua Magnum based cartridge demands the use of a custom or customized rifle with an appropriately cut chamber and fast-twist bore. The firearm action and if a repeating arm is required the magazine(s) must also be able to cope with dimensional increases.
An example of such a special .338 calibre extreme range bullet is the German CNC manufactured mono-metal 18.92 gram (292 gr) LM-105 (G1 BC ≈ 0.93 – this Ballistic coefficient (BC) is calculated by its designer, Mr. Lutz Möller, and not proven by Doppler radar measurements). If Mr. Möller's assumptions are correct, the LM-105 would have a supersonic range of ≈ 2000 m (2200 yd) at a muzzle velocity of 915 m/s (3,002 ft/s) under International Standard Atmosphere sea level conditions (air density ρ = 1.225 kg/m3). The 2010 version of the LM-105 bullet has an overall length of 54.3 mm (2.14 in) or 6.33 calibers and derives its exceptional low drag from a radical LD Haack or Sears-Haack profile in the bullet's nose area. Rifles chambered for this wildcat cartridge, with a cartridge overall length of 105 mm (4.13 in), and equipped with custom made 178 mm (1:7 inch) progressive twist rate 900 mm (35.43 in) long barrels with a 2° cone-angle (the standard C.I.P. cone-angle for the .338 Lapua Magnum is 6°) cone area finished first and second at several long range competitions. Its most recent win (2007) was in an international Special Forces and police sniper competition in Switzerland against rifles chambered for 7.62×51mm NATO up to .50 BMG at ranges from 100 m – 1,500 m (109 yd – 1,640 yd). The LM-105 bullet exhibited its very low wind drift susceptibility notably at ranges beyond 800 m (875 yd). A real world average G1 BC of ≈ 0.90 to 0.93 is commonly adopted by the users of this bullet, for making long range trajectory predictions using ballistics calculators.
The .343 Lapua Magnum LM-107 was a wildcat cartridge under development based on the standard .338 Lapua Magnum cartridge case. The LM-107 was hoped to boost the ballistic performance of the LM-105 by achieving an increase in supersonic range. The 19.3 g (298 gr) LM-107 projectile design is 59 mm long and has a Haack profiled nose and an Adams profiled tail. The rifling twist rate for the .343 Lapua Magnum LM-107 wildcat cartridge was chosen at 180 mm (1:7 inch), Ø lands = 8.72 mm, Ø grooves = 8.45 mm and loaded with the LM-107 projectile has a cartridge overall length of 107 mm. The length of the neck is increased from 8,31 to 8,50 mm to support the bigger LM-107 bullet. Several other dimensions of the .338 Lapua Magnum parental cartridge are also changed. The shoulder angle gets steepened from 40° to 60° and the body taper is set at 1°. The throat area is set at a 2° cone-angle. All this modifications make the .343 Lapua Magnum a fairly comprehensively revised wildcat cartridge. Out of a 900 mm (35.43 in) long progressive twist barrel Mr. Möller expected to achieve 909 m/s (2982 ft/s) muzzle velocity. If Mr. Möller's design assumptions are correct the LM-107 projectile with a calculated G1 BC of 1.02 will offer a supersonic range of ≈ 2170 m (2373 yd) at a muzzle velocity of 909 m/s (2982 ft/s) under International Standard Atmosphere sea level conditions (air density ρ = 1.225 kg/m3). However, the LM-107 project never materialized so there is no practical evidence to support these assumptions by Mr. Moller.
Read more about this topic: .338 Lapua Magnum, Supersonic Range Performance of The .338 Lapua Magnum
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