Bullet velocity: how much is enough?

The goal is always for faster bullet speed, but how much do you need and what are you willing to lose for it?

Many hunters are obsessed with bullet speed and worship at the altar of ultra-high velocity.

Scant consideration is given to bullet weight, ballistic coefficient (BC) and the great amount of propellant consumed, let alone muzzle disturbance, bore fouling and throat erosion.

Muzzle velocity — This deer was taken at long range with a 100gn Barnes X-Bullet from the .257 Roberts, which dropped it on the spot

Hunters and gun writers rarely mention the shooting problems associated with muzzle blast and recoil.

When it comes to taking game, particularly game at long distances, there are more things to be considered than bullet speed.

First, let’s take a look at big-game cartridges. A hunter influenced by all the high-velocity hype he reads, and who naturally covets the latest and greatest, buys a rifle for a king-size cartridge like the .30-378 Weatherby Magnum.

Let’s consider some hard facts. We’ll compare the giant .30-378 with the little .308 Winchester using, in both instances, a Nosler 180gn AccuBond bullet, a 24-inch barrel and 60,000psi chamber pressure.

In essence we will compare the smallest and slowest against the biggest and fastest popular bolt-action .30-calibre cartridges today.

Obviously, we cannot standardise on a powder because the same powders are not optimum for both cartridges. I tried to pick an optimum powder for each cartridge and settled on AR2218 for the .30-378 Wby Mag and AR2208 for the .308.

According to Load From A Disk, a compressed charge of 45gn of AR2208 provides 59,300psi chamber pressure and 2665fps muzzle velocity for the .308.

The .30-378 requires 112gn of AR2218 to get an almost identical pressure of 60,036psi chamber pressure for 3151fps.

That’s a 486fps advantage for the larger cartridge. What more needs to be said?

Using LFAD’s companion trajectory program, we can also compare downrange ballistic figures for 400 yards (366m) — the longest distance at which I consider a sporting maximum on big game. Let’s see how big an advantage the .30-378 offers over the lowly .308.

1. VELOCITY

At 400yd, the velocity for the .308 is 2007fps, while the .30-378 has 2421fps. There is still a huge velocity difference at this range, yet neither cartridge has enough impact speed for positive bullet upset with today’s bullets.

Shot placement is the most critical aspect of long-range shooting. Higher muzzle velocity does not help shot placement, but can actually hinder it

2. ENERGY

The .308 has 1610ft-lb of energy remaining at 400yd, while the .30-378 has 2342ft-lb. Both figures are adequate even for sambar or moose at that distance.

3. TRAJECTORY

With both rifles zeroed at 250yd (229m), the .308 is 19’ (48cm) low at 400yd according to the program, while the .30-378 is 13” (33cm) low. It’s not hard to hold a little high on an animal the size of a deer to make up the difference of 6” (15cm) at 400yd in the field.

4. WIND DEFLECTION

In a 16km/h crosswind the bullet from the .308 is blown 12” (30cm) off course while the .30-378 bullet is blown 9½” (24cm) off course. If you can guesstimate 2½” (6cm) at 400yd shooting from a hastily assumed field position and dope wind that precisely you’re a better shooter than I am.

5. RECOIL

Recoil with this load in a 3.9kg (8½lb) rifle-scope combination amounts to 22Nm (16.2ft-lb) in the .308 and 47Nm (34.4ft-lb) for a 4.2kg (9½lb) .30-378 — more than twice as much, which makes a big difference in having a rifle that’s mild to shoot and a rifle that the average shooter will find difficult to shoot accurately.

6. MUZZLE BLAST/PRESSURE

The .308 produces 490 bar (7119psi) of muzzle pressure. At 1087 bar (15,760psi) the .30-378 produces twice as much blast. Even the most blasé gun nut would have to admit that the larger round is very likely to cause flinching both in terms of blast and recoil.

Muzzle velocity and muzzle blast — Muzzle brakes do reduce recoil but they increase muzzle blast and lengthen an already long barrel. To the purist, they look ungainly

There are of course other drawbacks such as bore fouling and accelerated throat erosion, things that are harder to measure or calculate. Nonetheless, barrel life of the .308 is likely to give 3000 rounds of hunting accuracy while the .30-378 would be lucky to last 800 to 1000 rounds. Of course, if the .30- 378 rifle is used only for trophy hunting, it will last a lifetime.

The true believer will cry foul, saying that a 24-inch barrel is not standard for the .30-378 and a longer 26-inch barrel is needed to obtain the real advantage of the larger case. This is true.

And you can add a muzzle brake to reduce felt recoil, although it will increase the rifle’s muzzle blast to an uncomfortable level unless you wear ear muffs, and who wants to do that in the field?

It also increases barrel length and adds weight to an outfit that usually has a heavy barrel and large target-type scope so that recoil may be reduced a bit more.

Only a dyed-in-the-wool gun nut and velocity freak would plump for a heavy and cumbersome rifle that is awkward to handle, ill-balanced and a burden to carry. In fact, a rifle in .30-378 would have to weigh about 10kg to equal the recoil of a 4kg .308.

So we are talking about a rifle to take sambar-size game beyond the 400yd mark and you reckon the .308 is running out of steam at that distance. Experts agree that you need about 2000fps of impact velocity for positive bullet expansion and at least 1500ft-lb of striking energy for game the size of wapiti, moose and sambar.

But how many deer of any size have you ever taken at 400yd, let alone beyond that distance?

I can count the deer that I’ve taken beyond 200yd on one hand. Nor did I need a cartridge as large and powerful as the .30-378 Weatherby to do it.

The truth is that there are a lot of standard cartridges that do not require a heavy, ungainly rifle and are comfortable to shoot by the average hunter.

A standard-weight rifle chambered for a moderate cartridge like the .270 Winchester usually suits the average hunter best

I have used a wide selection of cartridges, including a number of magnums, and found downrange margins of effectiveness to be surprisingly small, without adding a longer barrel and heavier rifle for the larger cartridge.

While the large magnum benefits from a longer 26” barrel, the .308’s performance is not hampered that much by even a shorter 22” barrel. And the difference between a rifle with a 22” barrel and a 26” barrel definitely handicaps the foot hunter in thick country.

While this treatise compares extremes in cartridges, you will undoubtably find that an in-between cartridge will work best for you. Most shooters find that about 20-27Nm (15-20ft-lb) of recoil is their upper limit in a 3.9kg (8½lb) hunting rifle.

What it means is that something like the good old .270 Winchester, .30-06 or .280 Ackley Improved might be a better choice.

Today’s bullets are far more efficient than they were a few years ago. The Barnes X-Bullet construction, for example, offers bone-smashing power and deep penetration with less bullet weight than was once necessary. Bonded-core controlled-expansion designs from Nosler, Hornady and Swift have higher BCs and deliver excellent downrange performance.

Having said that, there is no question that higher velocity improves downrange energy, deflection and trajectory and that more powder drives the bullet faster. But how much more velocity does one need to gain a modest margin of practical advantage? And at what price?

The key factor in taking game at any distance is shot placement. A rifle that you can shoot well is one you are likely to do best with in the field.

While velocity is important, velocity alone does not give us the edge we are led to believe it does.