338309SP142 Technical Profile © Application: Target/Tactical

Barrel Bore Diameter: 0.330" 8.380 mm The diameter of the barrel from land to land.
Barrel Groove Diameter: 0.338" 8.590 mm The diameter of the barrel from groove to groove.
Bullet Weight: 309gr 20g Bullets are guaranteed to weigh within a quarter percent of the stated weight.
Bullet Length: 2.20" 55.940 mm
Tangent Ogive Length: 1.25" 31.775 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" 0.838 mm
Min Bullet Protrusion: 1.34" 33.950 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: 1.77" 45.000 mm
CIP and SAAMI cartridge overall length (COL) not observed or does not apply. Check the COL of your rifle for suitability with this bullet as described above. Check the magazine length of your rifle for suitability with this bullet.
Maximum M/V: 3600fps 1,097 m/s If the maximum muzzle speed is exceeded, dynamic stabilty problems may be encountered.
       

Twist Rates are guidelines but the Minimum Twist must be observed 
Twist: Sg = 1.4: 7.4" / 187 mm 22.3 Calibers The twist required to give a calculated Sg 1.4
Minimum Twist: 8" / 203.2 mm 24.2 Calibers The slowest twist required for stable flight and the best long range tractability more than 1090 yds or 1000 m. See the 'Notes' below.

Calculated Ballistic Coefficient - Standard Metro G1 profile
BC = 1.094 Maximum M/V to 2400 fps Maximum M/V to 732 m/s Any comparison with the BC values of other manufacturers is not valid as there is currently no standard method in use between manufacturers.  These BC values are only for use in an external ballistics program. Use the three values, as given, to approximately calculate BC for your launch speed and distance. For exact numbers, shoot drop tables at the elevation and temperature for your location.
BC = 0.937 2400 fps to 1200 fps 732 m/s to 366 m/s
BC = 0.682 1200 fps to 0 fps 366 m/s to 0 m/s

Suitable Cartridges, with consideration of the above specifications:

Barrel Size, twist rate, protrusion and launch speed may vary with different cartridges. Use the details above to determine whether this bullet is suitable for the cartridge.

NOTES
A Gyroscopic Stability (Sg) greater than 1.2 is required for SP bullets. For use under 720yds/660m an Sg of up to 1.5 or even greater can be used. For distances beyond 720yds/660m, 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.