| 2.2
Bigger Is Not Always Better
It is absolutely true that, if
two bullets are fired with the same muzzle velocity at the same
firing point and with the same weather conditions, the
bullet with the higher BC will arrive first at a specific target,
will have higher velocity and energy when it arrives, will suffer
less wind deflection, and will have less drop than the bullet with
the lower BC. This will happen regardless of caliber, bullet weight,
or bullet type. But notice the big IF condition in this statement.
If the bullets are fired with different muzzle velocities, at different
altitudes, or under different weather conditions, any conclusions
from the comparison may not be entirely correct.
What this means is that when comparing
the ballistic performance of different bullets, all the firing conditions
must be taken into account. Another very important consideration
is that when comparing bullet ballistic performance, the performance
must be evaluated for the purpose and objectives to be accomplished.
For example, the usual purpose may be target shooting or hunting.
If we wish to choose a bullet for the purpose of target shooting,
the main objectives are maximizing accuracy and minimizing wind
deflection. A very important advantage of handloading is that the
muzzle velocity produced by the cartridge can be adjusted so that
the gun delivers its best accuracy. Such a muzzle velocity is usually
a little less than the maximum safe velocity of the cartridge in
that gun, and this velocity usually must be discovered by trial
at the shooting range. Target shooters with modern high-power target
rifles generally are achieving accuracies on the order of 0.2 minutes
of angle (MOA) or less. On the other hand, shooting flat
is not very important, because the ranges to the targets are fixed
distances, sighting shots are usually allowed, and sights on guns
are allowed to be adjusted between stages of the matches. However,
sensitivity to crosswind is very important, because matches take
place under variable wind conditions. Even if a shooter is highly
experienced in estimating windage corrections, it is best that the
bullet selected for the match have the smallest practical sensitivity
to crosswind.
For hunting purposes shooting flat
is a major objective, as are adequate retained energy and momentum
over the effective range of the gun for the intended game, adequate
accuracy, and low sensitivity to crosswinds and vertical winds.
A gun that shoots flat produces small bullet drop within
the effective range for the intended game. This is very important,
because it is difficult for a hunter to estimate range to a game
animal under practical conditions in the field. Of course, there
are several optical and electro-optical range finders available,
but most hunters cannot be assured that their game will be patient
and stand perfectly still while they attempt to use a range finder
under non-hunter-friendly field conditions. The concept of point
blank range is one very practical way to ease the range-estimating
problem for hunters in the field (more about this in a later section).
A flat shooting gun inherently has more point blank
range than a gun with a rainbow trajectory. Flat
shooting requires high muzzle velocities and bullets with
high ballistic efficiency.
Adequate accuracy for hunting usually
means groups of 1.0 to 1.5 MOA for medium and large game, and 0.5
to 0.75 MOA for varmints. Wind sensitivity is very important, because
field environments typically have windy conditions. Crosswinds may
happen anywhere, and vertical winds are experienced in hilly or
mountainous regions. The wind deflection sensitivity of a bullet
to a vertical wind is exactly the same as its sensitivity to a crosswind.
In other words, suppose that a 1.0 mph crosswind from the shooters
right to left will cause a deflection of the bullet of, say, 6 inches
to the left at the target. Then a vertical wind of 1.0 mph upward
will also cause a 6 inch deflection of the bullet in the upward
direction. This is very important when shooting across a canyon
or along a hillside when the wind is blowing. To illustrate the points made above in
this subsection, we will consider two simplified examples, shown
in Tables 2.2-1 and 2.2-2. Two popular cartridges are used for these
examples. The first (see Table 2.2-1) is the 308 Winchester, also
known as the 7.62 x 51 mm NATO cartridge. This cartridge is very
popular for hunting medium game, such as deer and antelope. It is
also used for target shooting. For example, in Service Rifle competitions,
they are fired in the M14 and M1A rifles, and in Match Rifle competitions
they are fired in bolt action rifles. The second cartridge (see
Table 2-2-2) is the 300 Winchester Magnum. This cartridge is very
popular for both hunting large game, such as elk, moose and bear,
and for target shooting, particularly the Long Range target competitions.
These cartridges have been selected as examples because there is
such a wide variety of 30 caliber bullets available for handloading.
The examples are simplified in that the
numbers in Tables 2.2-1 and 2.2-2 are for sea level altitude and
standard atmospheric conditions. So, the performance of each bullet
is not calculated for realistic field conditions, but these examples
validly illustrate our key points. The numbers in the tables have
been calculated using Sierras Infinity Exterior Ballistics
Program.
Each table is for one of the two example
cartridges. Furthermore, each table is separated into two sections:
one for hunting purposes and the other for target purposes. In the
hunting purposes section, the first column in the table lists each
bullet selected for comparison. The next column contains the muzzle
velocity of each bullet. Each listed velocity is at or near the
top end of the velocity range for that bullet recommended in the
Reloading Data Section of this Manual for the cartridge in each
table. The third column lists the ballistic coefficient of each
bullet at the muzzle velocity. Later in this section we will describe
how BC varies with bullet velocity. The number in the table compares
the bullets at the muzzle velocity level for each. The BC variations
as the bullet flies are taken into account in the trajectory calculations.
The fourth column lists the energy of each bullet at the muzzle.
For hunting purposes it has been assumed
that the effective range of fire is 400 yards, that the rifle is
zeroed in at 250 yards, and that a telescope sight is used, with
the centerline of the telescope 1.5 inches above the cen-terline
of the bore. Then for these assumptions, the fifth column shows
the maximum bullet path height (sometimes called the maximum ordinate)
above the hunters line of sight through the telescope, together
with the downrange position from the muzzle at which this maximum
bullet path height occurs.
The remaining four columns in this section
of the table show ballistics properties at the 400 yard maximum
effective range point. Column 6 lists the remaining velocity; column
7 lists the bullet energy; column 8 lists the distance the bullet
passes below the hunters line of sight at 400 yards; and the
last column lists the wind deflection sensitivity that is,
the inches of deflection per mile per hour of either crosswind or
vertical wind. In the second section of Tables 2.2-1
and 2.2-2 for target shooting purposes, the first column lists the
target bullets selected for comparison; the second column shows
the muzzle velocity for each bullet; and the third column lists
the BC value at the muzzle velocity. Again, each listed velocity
is at or near the top end of the velocity range for that bullet
recommended in the Reloading Data Section of this Manual for the
cartridge in each table. For purposes of comparison, it is assumed
that a near-maximum load delivers the best accuracy, which is not
always true.
Two range distances are considered for
target shooting 600 yards and 1000 yards. Column 4 shows
the remaining velocity of each bullet at 600 yards, and column 5
lists the wind deflection sensitivity at 600 yards. Columns 6 and
7 show these same two parameters at 1000 yards from the muzzle.
Note that the wind deflection sensitivity values listed in the tables
are per mile per hour of crosswind or vertical wind. In other words,
if the wind speed is 10 mph, the bullets will deflect 10 times the
amount shown in the tables.
Consider first the 308 Winchester cartridge
in Table 2.2-1. For hunting purposes, the table shows that the bullet
that shoots flattest is the 150 grain SBT (Spitzer Boat Tail) at
2800 fps muzzle velocity. However, the bullet with minimum wind
deflection sensitivity is the 200 grain SBT at 2400 fps muzzle velocity.
So, the lighter 150 grain bullet with smaller BC passes about 4
inches closer to the line of sight at 400 yards than does the 200
grain bullet with a significantly higher BC. On the other hand,
the heavier bullet deflects considerably less in a crosswind or
vertical wind. If a crosswind or vertical wind speed were 10 mph,
the 150 grain bullet would be deflected 16.2 inches, while the 200
grain bullet would be deflected just 12.8 inches. So, the choice
of hunting bullets depends on which is more important to the shooter:
a flatter trajectory or sensitivity to wind conditions.
For target shooting purposes, the bullet
with the minimum wind deflection sensitivity in the 308 Winchester
cartridge is the 200 grain MatchKing fired at 2450 fps muzzle velocity.
In this case, the 200 grain MatchKing is better than the 220 grain
MatchKing just because the heavier bullet cannot be fired at a high
enough muzzle velocity. If the muzzle velocity of the 220 grain
bullet could be increased to around 2300 fps, then its higher BC
would give it less wind sensitivity than the 200 grain bullet. But
the cartridge does not have enough powder capacity to safely allow
the velocity increase.
For the 300 Winchester Magnum cartridge,
Table 2.2-2 shows that for hunting purposes the 180 grain SBT GameKing
bullet loaded to 3100 fps muzzle velocity shoots the flattest of
all five bullets listed. The 200 grain SBT GameKing bullet loaded
to 2900 fps has the least wind deflection sensitivity, but it is
just a tiny bit better than the 180 grain bullet. So, in this example
the numbers in the table indicate that the 180 grain SBT GameKing
bullet is probably the best choice for hunting. However, some hunters
Table 2.2-1 Ballistic Coefficient
Effects for the 308 Winchester Cartridge
| HUNTING |
PURPOSES |
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At 400 yds Range
(Zero at 250 yds) |
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| |
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| Selected |
Mzl Vel |
BC at |
|
Mzl Energy |
|
Max Bullet |
Velocity |
Energy |
Bullet |
|
Wind Drift |
|
| Bullet |
(fps) |
Mzl Vel |
|
(ft-lbs) |
|
Path (in) |
(fps) |
(ft-lbs) |
Path (in) |
|
(in/mph) |
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| |
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| 125 gr SPT |
3000 |
0.279 |
|
2498 |
|
3.43 @ |
1781 |
880 |
-19.33 |
|
2.09 |
|
| Pro-Hunter |
|
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143 yds |
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| 150 gr SBT |
2800 |
0.380 |
|
2611 |
|
3.68 @ |
1899 |
1201 |
-19.29 |
|
1.62 |
|
| GameKing |
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143 yds |
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| 165 gr SBT |
2600 |
0.404 |
|
2476 |
|
4.32 @ |
1810 |
1201 |
-21.93 |
|
1.62 |
|
| GameKing |
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139 yds |
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| 180 gr SBT |
2500 |
0.505 |
|
2498 |
|
4.49 @ |
1866 |
1391 |
-21.99 |
|
1.34 |
|
| GameKing |
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138 yds |
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| 200 gr SBT |
2400 |
0.552 |
|
2558 |
|
4.66 @ |
1832 |
1490 |
-23.36 |
|
1.28 |
|
| GameKing |
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136 yds |
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| TARGET SHOOTING
PURPOSES |
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At 600 yds Range |
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At 1000 yds
Range |
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| Selected |
|
Mzl Vel |
|
BC at |
|
Velocity |
Wind Drift |
Velocity |
|
Wind Drift |
|
| Bullet |
|
(fps) |
|
Mzl Vel |
|
(fps) |
(in/mph) |
(fps) |
|
(in/mph) |
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| 155 gr HPBT |
|
2800 |
|
0.450 |
|
1699 |
3.21 |
|
1170 |
|
10.81 |
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| Palma |
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| 175 gr HPBT |
|
2600 |
|
0.496 |
|
1648 |
3.13 |
|
1194 |
|
10.20 |
|
| MatchKing |
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| 180 gr HPBT |
|
2600 |
|
0.496 |
|
1650 |
3.14 |
|
1201 |
|
10.14 |
|
| MatchKing |
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| 190 gr HPBT |
|
2550 |
|
0.533 |
|
1664 |
2.97 |
|
1225 |
|
9.58 |
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| MatchKing |
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| 200 gr HPBT |
|
2450 |
|
0.565 |
|
1632 |
2.93 |
|
1230 |
|
9.31 |
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| MatchKing |
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| 220 gr HPBT |
|
2200 |
|
0.629 |
|
1504 |
3.04 |
|
1171 |
|
9.47 |
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| MatchKing |
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Table 2.2-2 Ballistic Coefficient
Effects for the 300 Winchester Magnum Cartridge
| HUNTING |
PURPOSES |
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At 400 yds Range
(Zero at 250 yds) |
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| |
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| Selected |
Mzl Vel |
BC at |
|
Mzl Energy |
|
Max Bullet |
Velocity |
Energy |
Bullet |
|
Wind Drift |
|
| Bullet |
(fps) |
Mzl Vel |
|
(ft-lbs) |
|
Path (in) |
(fps) |
(ft-lbs) |
Path (in) |
|
(in/mph) |
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| 165 gr SBT |
3200 |
0.404 |
|
3751 |
|
2.57 @ |
2294 |
1927 |
-13.72 |
|
1.21 |
|
| GameKing |
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144 yds |
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| 180 gr SBT |
3100 |
0.501 |
|
3840 |
|
2.65@ |
2373 |
2250 |
-13.61 |
|
0.98 |
|
| GameKing |
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142 yds |
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| 180 gr SPT |
3100 |
0.407 |
|
3840 |
|
2.79 @ |
2224 |
1977 |
-14.68 |
|
1.24 |
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| Pro-Hunter |
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142 yds |
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| 200 gr SBT |
2900 |
0.560 |
|
3734 |
|
3.06 @ |
2264 |
2276 |
-15.29 |
|
0.96 |
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| GameKing |
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141 yds |
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| 220 gr RN |
2750 |
0.310 |
|
3694 |
|
4.05 @ |
1809 |
1598 |
-21.28 |
|
1.89 |
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| Pro-Hunter |
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140 yds |
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| TARGET SHOOTING
PURPOSES |
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At 600 yds Range |
At 1000 yds
Range |
|
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| Selected |
|
Mzl Vel |
|
BC at |
|
Velocity |
Wind Drift |
Velocity |
|
Wind Drift |
|
| Bullet |
|
(fps) |
|
Mzl Vel |
|
(fps) |
(in/mph) |
|
(fps) |
|
(in/mph) |
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| 168 gr HPBT |
|
3200 |
|
0.462 |
|
2024 |
2.54 |
|
1379 |
|
8.61 |
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| MatchKing |
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| 180 gr HPBT |
|
3100 |
|
0.475 |
|
2026 |
2.46 |
|
1467 |
|
7.93 |
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| MatchKing |
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| 190 gr HPBT |
|
3000 |
|
0.533 |
|
2022 |
2.31 |
|
1491 |
|
7.46 |
|
| MatchKing |
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| 200 gr HPBT |
|
2900 |
|
0.565 |
|
1992 |
2.27 |
|
1497 |
|
7.24 |
|
| MatchKing |
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| 220 gr HPBT |
|
2750 |
|
0.629 |
|
1952 |
2.16 |
|
1505 |
|
6.82 |
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| MatchKing |
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| 240 gr HPBT |
|
2800 |
|
0.711 |
|
2078 |
1.82 |
|
1658 |
|
5.66 |
|
| MatchKing |
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|
prefer a flat base rather than a boat tail
bullet shape, and others prefer a round nose bullet for some game
in some terrain. So, Table 2.2-2 includes the 180 grain SPT (Spitzer)
Pro-Hunter bullet for direct comparison with the 180 grain SBT GameKing,
as well as the 220 grain RN (Round Nose) Pro-Hunter bullet. One
can see the 180 grain Spitzer flat base bullet has about 20% lower
BC than the 180 grain Spitzer boat tail bullet, and it loses velocity
and energy faster, and has about a 25% increase in wind sensitivity.
The 220 grain round nose bullet is the heaviest in the table, but
it has the lowest BC, loses velocity and energy rapidly as it flies,
has the worst trajectory curvature, and has the worst wind sensitivity.
This is a fine bullet for heavy game, but it rapidly loses its advantages
at longer ranges.
For target shooting with the 300 Winchester
Magnum, Table 2.2-2 shows that the best bullet is the 240 grain
MatchKing at 2800 fps muzzle velocity. This is the heaviest bullet
and has the largest BC. This illustrates a principle that many target
shooters have found generally true with magnum cartridges for target
shooting. That is, select the bullet with highest BC value and load
it as fast as it will go and still deliver maximum accuracy considering
recoil sensitivity of the shooter as well as accuracy capability
of the rifle.
So, considering
BC, bigger is sometimes better, but not always. The purposes of
the shooter, the shooting situation, and the limitations of the
gun and cartridge must be taken into account in choosing a bullet.
The best tool to use to examine all the possibilities is one of
the ballistics computation software programs for the personal computer.
All types of what if questions can be explored at the
keyboard.
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