"Life isn't about finding yourself. Life is about creating yourself." ~ George Bernard Shaw.

BULLET DATA

What detail and technical bullet data on GS Custom bullets do we get from the manufacturer on their website?
Apart from the basic data like Bullet Number, Bore Diameter, Groove Diameter and Suitable for Calibres (Subject to twist) detail, we also get the following technical data on the bullet which are essential for the reloader.

With the 308130HV bullet as example, let's look at the available technical data.

(a) The bullet's dimensions, i.e. Length (total bullet length) as well as it's Nose Length only, are given to us in both millimeters (mm) and inches (").
(b) Three different bullet speeds are indicated in both m/s (meters/second) and fps (feet per second); also
(bi) Three different BC values for each of the above three bullet speeds.
This comes in very handy when fed into a ballistic program to calculate the bullet's trajectory over different target distances.
(bii) Minimum Impact Speed in m/s and fps at which the HV bullet will expand reliably, is also given in the technical data.

These are important data for the reloader in order to know what to expect when using the specific bullet. As an example, if the specific bullet does not yield the minimum required impact speed over the planned hunting distance in your trajectory calculations, then obviously you should select another bullet that will yield at least the minimum impact speed over the planned hunting distance in order to achieve the best terminal ballistic results.

In the ballistic table below, this specific bullet still yields a velocity of 2548.7fps at 500m distance (Minimum impact speed = 1600fps.). Reliable expansion will therefor still take place at this distance and beyond, although normal hunting distances are most of the time well below 500m.

.308W
Altitude: 3000 ft    Temperature: 78 įF.
Bullet Weight:    130 gr    BC: 0.365.
Muzzle Velocity: 3150 fps    Zero Range: 250 meters.

Range Height Velocity Energy TOF
0 -1.50 3150.0 2864.0 0.000
50 1.08 3086.9 2750.4 0.053
100 2.56 3024.2 2639.7 0.106
150 2.91 2962.2 2532.6 0.161
200 2.07 2901.1 2429.3 0.217
250 0.00 2840.7 2329.2 0.274
300 -3.36 2781.0 2232.2 0.333
350 -8.07 2721.9 2138.4 0.392
400 -14.18 2663.5 2047.7 0.453
450 -21.76 2605.8 1959.9 0.515
500 -30.87 2548.7 1875.0 0.579

Then we also get Guidelines for Stability Factor & Twist Rate which are explained in a lot of detail and accompanied by a chart giving SF values for the particular bullet when launched out of a rifle with a specific twist rate.
Once again, if the required SF cannot be achieved with your rifle and it's twist rate over your planned hunting distances, please follow the advice given in the columns below, i.e. either select a shorter or longer bullet to achieve the SF requirements indicated for the specific hunting distance.

How do I know what is the minimum/maximum cartridge overall length (COL) that I can use with this bullet?
Follow the instructions in the COL columns below - simply add the minimum/maximum values given, to your cartridge case length.
In doing this exercise, you can determine the maximum COL that will fit your rifle's magazine best, as well as ensure proper feeding of the cartridge out of your rifle's magazine.

Finally, what is the minimum/maximum seating depths with this particular bullet?
With a little easy calculation one can easily get the answer to that question!

Minimum seating depth = Bullet length (1) or 29.6mm/1.17" minus Maximum value 21.0mm/0.83" (3) = 8.6mm/0.34".

Maximum seating depth = Bullet length (1) or 29.6mm/1.17" minus Minimum value 18.0mm/0.71" (2) = 11.6mm/0.46".

The barrel's vibration can be fine tuned by adjusting the COL between the above minimum and maximum seating depths of the bullet in the brass case. In so doing you should be able to achieve the smallest possible group on the target with the particular bullet, after having complied with your rifle's specific preferences on COL.


.308" 130gr HV
 
Bullet Number Bore Diameter Groove Diameter Suitable for Calibres (Subject to twist)
308130HV080 7.62mm 0.300" 7.82mm 0.308" 308 Win, 7.62 UKM, 7.82 Warbird, 7.62 Nagant, 30 Picra, 30-06, 300 Mag H&H, Lapua, RUM, Wea, Win, WSM, 30-284, 30-30Win, 303 Sav, 300 Sav, 30-40 Krag, 307Win, 308EH, 308 Norma Mag, 30Fl N.E., 30R Blaser, 30 Super Fl H&H.
Length (1) Nose Length Weight
29.6mm 1.17" 16.0mm 0.63" 130gr 8.4g
Speed 1006m/s 3300fps 747m/s 2450fps 488m/s 1600fps Min Impact Speed
BC .370 .355 .352 488m/s 1600fps
Guidelines for Stability Factor, Twist Rate and COL:

Choose a bullet length best suited to your rifle twist and type of hunting.

Note that S/F increases as twist tightens.  A 1:10" twist is tighter than a 1:12" twist.

Bush and dangerous game hunting

S/F greater than 1.6 is required. There is no upper limit to the S/F here. If this bullet does not meet the requirement, use a shorter bullet.

General hunting to 500m/yds

S/F greater than 1.4 is required. There is no upper limit to the S/F here. If this bullet does not meet the requirement, use a shorter bullet.

Long range beyond 500m/yds

S/F greater than 1.1 is required but more than 1.5 is not desirable. If this bullet S/F is too high, use a longer bullet. If too low, use a shorter bullet.

COL: To determine the minimum and maximum cartridge overall length with this bullet, add the minimum or maximum values to your cartridge case length.

Minimum 18.0mm / 0.71" (2)
Maximum 21.0mm / 0.83" (3)
On the chart to the right:

1. Select the twist rate of your rifle on the horizontal axis and read the S/F on the vertical axis.

2. Use the guidelines above to determine suitability for your application.

3. Check the calibre list for your calibre.


GS Custom Bullets is the only manufacturer of monolithic premium grade bullets who specifically requires that users should select the correct length bullet to fit their rifle barrels' twist rate in order to achieve the best results with GSC bullets.
As a matter of fact, all other bullet manufacturers market their bullets according to bullet weight without giving much attention to the bullet's length.

Why would this bullet length thing be so important?
As GS Custom explains it:
"Your rifle calibre dictates the diameter of the bullet you must use. Similarly, the rate of twist dictates the length of the bullet that must be used. Selecting a bullet by weight, rather than length, makes as much sense as choosing a pair of shoes by weight rather than shoe size."

What is the final result when selecting the correct length bullet for your rifles' twist rate?
Again as per GS Custom:
"It is important to match the bullet length correctly with the twist rate of your rifle and with the intended range distance in mind. This is more likely to ensure good terminal ballistics than the traditional, but unscientific, method of choosing a bullet by weight."
Note that a third requirement is brought into the equation, namely: "intended range distance" over which you intend to hunt.

Nou kom die logiese vraag op: "Maar hoe voeg ek nou al die goed saam om uiteindelik die korrekte lengte koeŽl vir my geweer se spiraal en die afstand waaroor ek beplan om te jag, uit te kies?"

Die bostaande data oor die betrokke koeŽl wat beskikbaar gestel word, sal u lei na die regte keuse koeŽl wat by u geweer se spiraal sal pas - diť koeŽl sal ook die verlangde SF oplewer om die beste moontlike resultate te kan behaal met die GSC koeŽl in u geweer.

Sů, what about bullet weight? That follows automatically and is not really of great importance - having dealt correctly with twist rate, bullet length and intended hunting distance - your calibre rifle will deal successfully with game that is normally hunted with that type of rifle.

Kontak ons gerus indien u nie seker is van u koeŽl keuse nie, meer inligting verlang oor die hele prosedure of enige vrae hieromtrent het wat by u mag ontstaan.

Terminology -
Twist rate = spiraal (uitgedruk as: loop met spiraal van 1:10" byvoorbeeld.)


I've learned .... That one should keep his words both soft and tender, because tomorrow he may have to eat them. ~ Andy Rooney.