Where that bullet lands depends more on marksmanship than on the barrel’s inherent accuracy.
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.