Sierra’s 5th Edition Manual Exterior Ballistics Section

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 shooter’s 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 Magnums. 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 Sierra’s 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 centerline of the bore. Then for these assumptions, the fifth column shows the maximum bullet path height (sometimes called the maximum ordinate) above the hunter’s 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 hunter’s 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 cartridges 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 cartridges 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.

Table 2.2-1 Ballistic Coefficient Effects for the 308 Winchester cartridges

HUNTING	PURPOSES
												At 400 yds Range (Zero at 250 yds)
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)
125 gr. SPT	3000		0.279			2498				3.43 @		1781		880		-19.33			2.09
Pro-Hunter										143 yds
150 gr. SBT	2800		0.380			2611				3.68 @		1899		1201		-19.29			1.62
GameKing										143 yds
165 gr. SBT	2600		0.404			2476				4.32 @		1810		1201		-21.93			1.62
GameKing										139 yds
180 gr. SBT	2500		0.505			2498				4.49 @		1866		1391		-21.99			1.34
GameKing										138 yds
200 gr. SBT	2400		0.552			2558				4.66 @		1832		1490		-23.36			1.28
GameKing										136 yds
TARGET SHOOTING PURPOSES
											At 600 yds Range					At 1000 yds Range
Selected				Mzl VEL			BC at				Velocity		Wind Drift			Velocity				Wind Drift
Bullet				(fps)			Mzl VEL				(fps)		(in/mph)			(fps)				(in/mph)
155 gr. HPBT				2800			0.450				1699		3.21			1170				10.81
Palma
175 gr. HPBT				2600			0.496				1648		3.13			1194				10.20
MatchKing
180 gr. HPBT				2600			0.496				1650		3.14			1201				10.14
MatchKing
190 gr. HPBT				2550			0.533				1664		2.97			1225				9.58
MatchKing
200 gr. HPBT				2450			0.565				1632		2.93			1230				9.31
MatchKing
220 gr. HPBT				2200			0.629				1504		3.04			1171				9.47
MatchKing

Table 2.2-2 Ballistic Coefficient Affects for the 300 Winchester Magnum Cartridges

HUNTING	PURPOSES
								At 400 yds Range (Zero at 250 yds)
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)
165 gr. SBT	3200		0.404		3751		2.57 @	2294	1927	-13.72		1.21
GameKing							144 yds
180 gr. SBT	3100		0.501		3840		2.65@	2373	2250	-13.61		0.98
GameKing							142 yds
180 gr. SPT	3100		0.407		3840		2.79 @	2224	1977	-14.68		1.24
Pro-Hunter							142 yds
200 gr. SBT	2900		0.560		3734		3.06 @	2264	2276	-15.29		0.96
GameKing							141 yds
220 gr. RN	2750		0.310		3694		4.05 @	1809	1598	-21.28		1.89
Pro-Hunter							140 yds
TARGET SHOOTING PURPOSES
							At 600 yds Range		At 1000 yds Range
Selected		Mzl VEL			BC at		Velocity	Wind Drift	Velocity			Wind Drift
Bullet		(fps)			Mzl VEL		(fps)	(in/mph)		(fps)		(in/mph)
168 gr. HPBT		3200			0.462		2024	2.54		1379		8.61
MatchKing
180 gr. HPBT		3100			0.475		2026	2.46		1467		7.93
MatchKing
190 gr. HPBT		3000			0.533		2022	2.31		1491		7.46
MatchKing
200 gr. HPBT		2900			0.565		1992	2.27		1497		7.24
MatchKing
220 gr. HPBT		2750			0.629		1952	2.16		1505		6.82
MatchKing
240 gr. HPBT		2800			0.711		2078	1.82		1658		5.66
MatchKing

However, some hunters 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 Magnums, 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.