308137SP157 Technical Profile    Application: Target/Tactical

Barrel Bore Diameter: 0.300" 7.620 mm The diameter of the barrel from land to land.
Barrel Groove Diameter: 0.308" 7.820 mm The diameter of the barrel from groove to groove.
Bullet Weight: 137gr 8.9g Bullets are guaranteed to weigh within 0.25% of the stated weight.
Bullet Length: 1.25" 31.820 mm
Secant Ogive Length: 0.60" 15.276 mm These dimensions are critical to consistent external ballistic performance and are held constant to within 0.005 mm (0.0002")
Meplat Diameter: 0.03" 0.762 mm
Min Bullet Protrusion: 0.68" 17.340 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: 0.87" 22.000 mm
Bullet conforms to CIP and SAAMI for magazine length. Check the magazine length of your rifle for suitability with this bullet.
Maximum M/V: 3200fps 975 m/s If the maximum muzzle speed is exceeded, dynamic stabilty problems may be encountered.
Twist: Sg = 1.5: 11.0" / 278 mm 36.4 Cal. in length The twist required to give a calculated Sg 1.5
Minimum Twist: 12" / 304.8 mm 40.0 Calibers in length The twist required for stable flight and the best long range tractability more than 440 yds or 410 m. See the 'Notes' hereunder.

Calculated Ballistic Coefficient - G1 profile

BC = 0.415 Maximum to 2200 fps Maximum to 671 m/s BC values are calculated at standard Metro values using a G1 profile.  Any comparison with the BC values of other manufacturers is not valid as there is currently no standard method in use between manufacturers.  Enter these values into an external ballistics program to calculate BC for your launch speed and distance. For excact values, shoot drop tables at the elevation and temperature for your location.
BC = 0.379 2200 fps to 1200 fps 671 m/s to 366 m/s
BC = 0.272 1200 fps to 0 fps 366 m/s to 0 m/s

Suitable Cartridges, with consideration of the above specifications:

.308" Calibers


A Gyroscopic Stability (Sg) greater than 1.2 is required for SP bullets. For use under 440yds/410m an Sg of up to 1.5 or even greater can be used. For distances beyond 440yds/410m, 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.