Slap a ruler on the muzzle of any rifle in your rack, and it will likely measure between .540 and .900. At least, that’s the range of diameters from a random sampling here. Those .540 barrels are pretty slim — at least for 30-bores, where wall thickness runs less than .120.

“I’ve printed half-minute knots with 26-inch .300 Weatherby barrels miking .560 at the muzzle,” said my friend D’Arcy Echols, some years ago. He builds carriage-class hunting rifles, many chambered for magnum rounds. A hull as big as a perfume bottle looks downright intimidating next to a barrel with walls not much thicker than a fuel line’s.

Over the last decade D’Arcy has leaned to barrels with more beef. “I prefer .600 muzzles on 26-inch .30 magnums now. If a client wants flutes, I’ll make it .700. Fluting trims weight without sacrificing stiffness. Of course taper matters. A steep taper at the chamber, with a near-parallel sweep from there to the muzzle, can leave you with a pretty limber barrel. Gradual tapers add spine.”

Why would you want a .300 Magnum with a lightweight barrel? Mainly, to carry the rifle easily on long hikes in steep places. You’ll take one shot, or two. The barrel will never get warm enough to melt frost, so the spread of shots exiting a tube with the glow of fresh lava matters not. Like small binoculars, slender barrels are for hunters who move a lot but apply their gear just once in awhile. If you’re setting up to glass coyotes for a term spanning four episodes of Downton Abbey, bigger glass is worth hauling to yon rim. It makes looking more comfortable and more effective. When your mission is to empty an ammo can into a poodle pasture before noon, a heavy barrel makes sense. It counters the warping effect of heat and helps you steady the rifle to hit small, distant targets.

Logic tells you thick-walled barrels vibrate less violently during bullet passage than light barrels. You’d also expect a thick tube to serve as a heat sink during prolonged fire. With the stiffness afforded by its greater mass, the slower heating of thick steel means you’re less likely to get impact shift after a few rounds. Heavy barrels don’t “walk” as readily as lightweights.

But one shot through a cold bore — or two or three — can be as predictable from a slim barrel.

Outside diameter doesn’t define light barrels or heavy. Bore diameter figures in. An early Mauser barreled by the late, talented Maurice Ottmar has a .720 muzzle. But wall thickness there is barely .130! This .458 Magnum points like a shotgun. With 500-grain solids, it also belts me like a wrecking ball. If it didn’t punch neat cloverleafs and hit intuitively where I look, it would have to sleep elsewhere. The heft and balance that bring its bead instantly, unerringly on target derive mainly from just-right barrel contour. Heavier, this 24-inch tube would make the rifle sluggish; a lighter barrel would bound all over the place offhand, and no doubt leap from my grasp in recoil.

D’Arcy Echols maintained a .130 wall — which he considers minimum — with a slim .537 muzzle on a .270 rifle. He’s turned barrels to .523 for a .257 Roberts and a 6.5/06. Each of these three sporters weighs less than 8 pounds, scoped and loaded, but can keep three shots inside .75 MOA! “The barrels are all free-floated,” he adds. “Some shooters think light barrels need upward pressure near the forend tip, but I’ve found otherwise. Besides, under changing conditions, such pressure can vary. Over time, the barrel’s resistance will weaken the lift of the forend.”

For any given O.D., short barrels have more spine than long ones. The 26-inch barrel useful on a .300 Weatherby, to burn a tall column of slow powder, isn’t necessary on a “walking varminter” in .22-250 or .243. The .257, 6.5 and .270 tack-driving lightweights from Echols’ shop wear 22-inch tubes. They are stiffer than the longer .300 barrel with identical wall thickness at the muzzle. This principle is easy to see in archery. An aluminum arrow of the proper spine (diameter and wall thickness) is correct for a given draw weight only at a given length. Trim a couple of inches from the shaft, and diameter or wall thickness must be reduced. Increase draw length, and you achieve proper spine with larger or thicker-walled shafts.

Stiffness is one reason some bolt-action handguns can print one-hole groups. To match the spine of a 12-inch barrel in a 24-inch tube for a rifle, you’d have to make it impractically heavy. The corollary: “Efficient” cartridges with modest charges of fast-burning powder have an edge on “over-bore-capacity” rounds burning handfuls of slow fuel. A .22 LR bullet, for example, reaches top speed after only 16 inches of bore travel. A longer barrel just adds friction. Drag. A .220 Swift load fired from a 16-inch barrel could light a charcoal grill several paces from the muzzle. Well, almost.

Small-bore cartridges have an obvious advantage if you crave stiff but lightweight barrels. You needn’t put much steel around a .22 or .17 missile to fashion a rigid tube. To match that spine with bullets the diameter of macadamia nuts, you’ll need many pounds of barrel alloy. Double-barrel “stopping rifles” are hopelessly handicapped by their gaping bores in twin tubes. Thick walls would make them hard to lift, aim or swing. But regulating these thin-walled barrels to hit a single point of aim at, say, 50 paces, drives otherwise sane men to seek therapy. A couple of shots from one side stretches that barrel, affecting bullet placement from the other. “A quick right and left” still proves effective on dangerous beasts because they are dangerous only when close, where half-minute accuracy matters as much as the color of your socks.

I once thought heavy barrels were worth their weight on bolt rifles, that if the object was to deliver an accurate shot, anything that enhanced accuracy was an asset. Age and experience have changed my view. Excepting barrels on rifles relegated to sustained or rapid fire, slender barrels now seem a better choice. Slim, lightweight hunting rifles can put first shots on target as reliably as 12-pounders. Hunting, the first shot matters most. Where that bullet lands depends more on marksmanship than on the barrel’s inherent accuracy. Second and third shots can count when you’ve surprised a troupe of coyotes, or when you’ve bungled your first try. But until you reach the last round in an ordinary magazine, deliberate fire from that lightweight barrel still matches the accuracy you can expect from stiffer tubes.

The proper dimensions of a barrel can’t all be determined by math. Rifle balance and felt recoil figure in. Ditto your shooting and hunting style. I’ve tested rifles that weighed less than 5 pounds. They were, predictably, a delight on steep trails. Not so when I tried to steady one in a brisk wind or after a fast ascent, my breath coming in gasps. When I triggered a frisky load, the pencil-thin barrel would whip up as if yanked from the heavens, the rifle’s comb cracking my molars.

Mass in the barrel can help you shoot more accurately and more comfortably. It helps steady the rifle on target and absorbs recoil. I’ve come to think a bolt rifle for hunting predators or big game should weigh about 8 pounds, trailside. Given proper balance, such a rifle is easy to carry and quick on target, but it has enough mass to keep the bounce from my racing pulse and quivering muscles within reasonable limits as I snug the sling for a shot or take offhand aim up close. There’s enough heft to throttle the kick of .30-06-class rounds and permit fast follow-ups coming out of recoil. For me, the best barrel contour has less to do with its effect on bullets than how the rifle affects my mobility and marksmanship.

Like many riflemen, I’ve concluded that for hunting predators or big game, the average measure of five-shot, hot-barrel groups is largely academic.