Bullet Selection for the .308 Winchester:
.....................Hunting Applications

...The 308 Winchester is an incredibly versatile round for hunting.  In order to take advantage of the cartridges versatility, the hunter has to make the right choices about the bullet being used for the intended game and range at which it will be shot.  Beyond external ballistic performance which determines the bullets trajectory, there’s terminal ballistics to consider.  What the bullet does when it impacts game is extremely important to the outcome of a hunt.  There are many schools of thought on bullet penetration and expansion.  To begin, let’s take a look at the external ballistic performance that’s typical for a modern hunting rifle in .308 Winchester.

Figure 1 is a depiction of a representative hunting rifle that might be chambered in .308 Winchester.  For this analysis, the muzzle velocity and recoil level will be based on the typical .308 hunting rifle with a bolt action and a 26” barrel.  Included in Figure 1 is the full line of Berger VLD Hunting bullets that are available for, and will work in the average bolt action .308 Winchester hunting rifle.  The BC of the bullets and the minimum twist required for stability are shown in addition to the muzzle velocity and recoil generated by a load that produces a 60,000 psi max chamber pressure.  Such loads should be considered the upper limit to what the .308 Winchester is capable of achieving.

Most .308 hunting rifles have barrels with twist rates between 1:10” and 1:12” which means they’re usually adequate to stabilize most bullets.  If you choose to shoot the 210 grain VLD in a hunting rifle, first verify that your barrel has at least a 1:11” twist.

As you can see from the data in Figure 1, the 60,000 psi of peak chamber pressure generates higher velocity for the lighter bullets and more recoil for the heavier bullets.  This is the first point to consider when choosing a bullet; recoil.  If you or a young shooter that you’re loading for is overly sensitive to recoil then you’ll want to select a lighter bullet.  Understanding the ballistic performance of the lighter bullet will be important to the proper use and effectiveness of the rifle system.

If recoil is not a consideration, then the question becomes: “what bullet will deliver the best performance on the intended game?”  The term best performance needs to be defined better.  The terminal performance of the bullet is important and that will be addressed soon, but first consider the external ballistics of the bullet.  After all, the terminal performance of the bullet is set up by how accurately and efficiently the bullet arrives at the target.  To begin the bullet selection process, let’s consider the external ballistics.

The two major factors of external ballistics to consider are gravity drop and wind deflection.  How much a bullet drops is a matter of how far away the target is.  In order to hit a target at long range, you have to know how much the bullet drops at that range so you can apply an aiming correction.  In hunting situations where the target is far enough away that you have to apply an aiming correction (past 200 yards) and you have to guess how far away the target is, it’s important that the bullet has a flat trajectory, meaning it remains close to the line of sight for a long distance.  A flat trajectory will minimize the effects of errors in range estimation.  The lighter bullets at high speed will have flatter trajectories (out to some distance) compared to heavier bullets.  The conclusion of the preceding discussion is: lighter bullets can achieve higher muzzle velocities and will fly flatter trajectories which make it easier to hit targets when the range is uncertain.

If you’re hunting with a laser rangefinder and can measure the range to the target exactly, then a flat trajectory isn’t important.  The next uncertainty to consider is wind deflection.  Wind deflection can be much more than people commonly think, certainly enough to cause a miss or a poorly placed shot on an animal at long range.  In order to minimize the miss distance due to wind deflection, you want a bullet that is most resistant to wind deflection.  When loaded to equal chamber pressures, heavier bullets are more resistant to wind deflection than lighter bullets.

The two previous paragraphs point out the fundamental trade off in external ballistics for light bullets compared to heavy bullets.  Light bullets are flatter, but heavy bullets are more resistant to wind deflection.

Another consideration to make is lethality.  Which bullets are most lethal on game?  Berger VLD bullets penetrate several inches of tissue and then rapidly expand and fragment inside the animal’s vitals.  This behavior is reliable down to impact speeds of 1800 fps.  The lethality of a bullet impact is proportional to its impact velocity and the mass of the bullet (bigger and faster is better).  According to the lethality chart for the 308 Winchester, the heavier bullets are lethal on all sizes of game at longer ranges than lighter bullets.  The reason is because the heavy bullets retain their velocity better, and have more mass.  The result is a higher energy, and more lethal impact.

In light of the above considerations, the following blanket statement can be made about bullet selection for hunting applications:
Choose the heaviest bullet possible, with the following considerations:

1. Make sure your barrel can stabilize it.
2. Make sure you’re comfortable with the recoil.
3. Make sure you can achieve acceptable accuracy with the heavy bullet from your rifle.

For example, if you’re barrel has a 1:12” twist, you can’t stabilize the 210 grain VLD.  The heaviest you can go is the 190 grain, so start there.  Or, if your barrel has a 1:11” twist, but it’s a light weight rifle and you’re not comfortable with the recoil of the heavy 190 and 210 grain bullet, then the 168, 175, or 185 grain VLD may be a better choice.  As a final example; if you have a 1:11” twist barrel, a heavy rifle that you can tolerate recoil with, but the heavy bullets just don’t group well in your rifle, then you should choose a bullet that shoots acceptably small groups because the inherent accuracy of your rifle is more important than a slight edge in ballistics.

Notice that the kinetic energy of the 155 and 210 grain bullets is equal at the muzzle (the 210 grain bullet achieves a slower muzzle velocity than the 155).  At 500 yards, the 210 VLD has almost a 300 foot-pound advantage in energy compared to the 155 grain VLD (1506 ft-lb vs 1206 ft-lb).  Also note the retained velocity.  At the muzzle, the 155 grain VLD is 401 fps faster than the 210 grain VLD (2850 fps vs 2449 fps).  However, at 500 yards, the 155 has lost much more velocity than the 210, and is only 82 fps faster (1880 fps vs 1798 fps).  By 700 yards, the 210 VLD actually has more retained velocity than the 155 VLD by 13 fps.  The velocity advantage continues to grow in favor of the heavy 210 grain bullet at longer ranges.

Some shooters believe that the .308 Winchester is not a big enough case to generate “high enough” velocity with bullets as heavy as 210 grains.  That’s not necessarily true.  The heavy bullets retain velocity much better than light bullets, and can strike with more energy and velocity at long range than the lighter bullets which started out faster.  As long as you can achieve good accuracy with the heavy bullets at moderate muzzle velocities, there’s no reason not to use them for hunting in cases as small as the .308 Winchester.

In conclusion, heavy bullets are better ballistic performers than light bullets in the categories of; resistance to wind deflection and lethality.  Lighter bullets have an advantage by being able to shoot a little flatter trajectory than heavy bullets.  If you’re using a rangefinder to eliminate range uncertainty, then the flat trajectory is less important, and the heavier bullets are the clear choice.

 

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