The rifle wasn’t grouping well. We went downrange for a closer look.
“Should shoot better than this,” my friend said as we studied the 3-shot, 2-inch group. “It’s been blueprinted, custom barrel, the works.”
“Don’t those holes look a bit big for .243?” I pointed out.
“Uh…” He leaned closer. “Yeah. And they’re crooked. Look more egg shaped than round.”
“You’re shooting a 6mm Remington, right?”
“Hundred-grain Nosler Partition.”
“There’s your problem.”
“The Nosler’s are no good?”
“No. They’re too long. I’m betting the barrel’s twist rate is too slow to stabilize them.”
It was. When we ran a tight brush down the bore and measured the distance over which the cleaning rod made a complete turn, it was once in 12 inches. Remington had put 1-12 twist barrels on its original .244 Remington cartridge way back in 1955. It’s a fine rate of twist for stabilizing most 85-grain or lighter bullets, but go much heavier than that and bullets become too long to stabilize. Remington reissued the .244 cartridge as the 6mm Remington in 1963, giving it a 1-9 twist, but it was too late. American shooters had fallen in love with Winchester’s ballistically similar .243 Winchester, which started life with a 1-10 twist barrel, sufficient for stabilizing 100-grain bullets.
Ordinarily, hunters don’t have to concern themselves with rifling twist rates. Manufacturers use enough twist to stabilize the longest bullets popularly loaded in most cartridges. But today’s latest low-drag, long-range, high B.C. bullets are stretching length as much as possible, and that can cause problems in some barrels. So can monolithic copper alloy bullets. Copper is less dense than lead, so copper bullets of equivalent weight must be longer.
Handloaders will find warnings about long bullets and twist rates on bullet boxes, but as more and more long range bullets are put on the market, we could start seeing factory ammunition pushing the boundaries of standard twist rates. I predict that soon those traditional twists will be giving way to faster ones, especially in some popular extreme-range calibers.
There’s no need to panic, but if you notice a pet rifle — or even a new one — shooting poorly, study those bullets holes for roundness. If they aren’t perfectly round, the bullet wasn’t stable in flight. Instead of spinning nicely on its center, it was wobbling like a poorly thrown football. Your rifling twist rate is likely too slow to stabilize those bullets. If you want accuracy, you’ll have to shoot shorter bullets or rebarrel the rifle, using a faster twist rate.
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