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The C.I.P. recommends a five groove barrel contour with each groove having an arc length of 5.33 mm (0.210 in) and a twist rate of one revolution in 406 mm (16.0 in). The recommended pressure for the .505 Gibbs is 2,700 bar (39,000 psi).
SAAMI recommends a barrel rifling contour of 6 grooves with a bore Ø of .2505 in (6.36 mm) and a groove Ø of .257 in (6.5 mm) with each groove being .098 in (2.5 mm) wide. The recommended optional twist rate is one revolution in 10 in (250 mm). Both SAAMI and Weatherby recommend a freebore of .378 in (9.6 mm).
There are a number of sizes listed below that appear to be quite similar, and while the tolerances of these connectors are typically indicated as ±0.05 or ±0.03 mm by the manufacturers, there is still ambiguity as to whether two sizes differing by only 0.05 mm (or where the specification is only given to the nearest 0.10 mm) warrants listing ...
Conventional eight groove rifling on the left, and octagonal polygonal rifling on the right. Polygonal rifling (/ p ə ˈ l ɪ ɡ ə n əl / pə-LIG-ə-nəl) is a type of gun barrel rifling where the traditional sharp-edged "lands and grooves" are replaced by less pronounced "hills and valleys", so the barrel bore has a polygonal (usually hexagonal or octagonal) cross-sectional profile.
The addition of a flash hider to the barrel of the M110, which also necessitates a modified QD Suppressor unit similar to that on the Mk 11. The M110's use of KAC's one-piece 30 mm scope mount instead of two separate scope rings. On June 12, 2008, the M110 was ranked #2 on the U.S. Army's top ten inventions of 2007. [5]
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Values courtesy of the Hornady Ballistic Calculator [14] For the purposes of this comparison barrel a barrel length of 24 in (610 mm) is used. The .458 Lott is able to attain over 2,300-foot-per-second (700 m/s) with a 500-grain (32 g) jacketed bullet at safe pressure levels from a 23–24-inch (580–610 mm) barrel.
A small number of the early models featured a stepped barrel contour as well as a demilled bayonet lug. [12] Measurements on the stepped barrel's rifling were as long as the non-stepped barrel, revealing that the stepped barrel is not simply a shorter F2000 military barrel with an extended muzzle brake which is similar to the PS90. [12]