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408385SP144 Technical Profile    Application: Target/Tactical

Barrel Bore Diameter: 0.401" 10.185 mm The diameter of the barrel from land to land.
Barrel Groove Diameter: 0.408" 10.362 mm The diameter of the barrel from groove to groove.
Bullet Weight: 387gr 25.1g Bullets are guaranteed to weigh within 0.25% of the stated weight.
Bullet Length: 1.99" 50.550 mm
Secant Ogive Length: 1.08" 27.482 mm These dimensions are critical to consistent external ballistic performance and are held constant to within 0.005 mm (0.0002")
Meplat Diameter: 0.04" 1.019 mm
Min Bullet Protrusion: 1.16" 29.460 mm Add the case length to these numbers to determine the maximum and minimum cartridge overall length that is possible with this bullet.
Max Bullet Protrusion: 1.54" 39.000 mm
Bullet does not conform to CIP and SAAMI for magazine length. Check the magazine length of your rifle for suitability with this bullet.
Maximum M/V: 3000fps 914 m/s If the maximum muzzle speed is exceeded, dynamic stabilty problems may be encountered.
       
Twist: Sg = 1.5: 13.0" / 323 mm 31.8 Cal. in length The twist required to give a calculated Sg 1.5
Minimum Twist: 14" / 355.6 mm 34.9 Calibers in length The twist required for stable flight and the best long range tractability more than 530 yds or 490 m.
       
Calculated Ballistic Coefficient - G1 profile  
BC = 0.772 3000 fps to 2100 fps 914 m/s to 640 m/s BC values are calculated at standard Metro values and serve as a comparison between GSC bullets.  Any comparison with the BC values of other manufacturers is not valid as there is currently no standard method in use between manufacturers.
BC = 0.712 2100 fps to 1200 fps 640 m/s to 366 m/s
BC = 0.515 1200 fps to 0 fps 366 m/s to 0 m/s

Suitable Cartridges, with consideration of the above specifications:

All .408" cartridges, subject to the above specifications as well as bores including the .408" LRB.

NOTES

A Gyroscopic Stability (Sg) greater than 1.2 is required for SP bullets. For use under 530yds/490m an Sg of up to 1.5 or even greater can be used. For distances beyond 530yds/490m, the Sg can be decreased with a slower twist, but never less than 1.2 for GSC SP bullets.
*Note that Sg increases as twist tightens.  *A 1:10" twist is tighter than a 1:12" twist within a given caliber only. *Twist rates given in caliber lengths can be compared across calibers. *Choose a bullet length best suited to your rifle twist and type of shooting.  *When a bullet is specified for a given twist rate, it can also be used in any twist that is tighter.  Using it in a slower twist than specified, is not advisable. *Some experimentation will be required to determine exact drop tables for your equipment and location.