The Firing Line Forums - View Single Post - 1:12 twist won't stabilize 180gr in a 300wm?

Bart B. · January 8, 2013, 01:29 PM

Bullet stabilization's all about how many rpm's the bullet spins at for a given muzzle velocity.

Winchester loads 180's in .308 Win. ammo leaving at 2600 fps in their rifle's 1:12 twist barrels. They're well stabilized. So were the Western Cartridge Company's 197 and 200 grain match bullets made to shoot over 100 fps slower from Win. 70 match rifles chambered for the .308 Win. and 1:12 twist barrels.

So were the 180 grain Sierra HPMK's from the Army's M14NM's in competition leaving a bit faster in their 1:12 twist barrels. And they won their share of matches and set a few records with that load. They too, were well stabilized. And the 190 Sierra HPMK's the USN and USAF teams shot from their 7.62 NATO M1's leaving about 2600 fps from their 1:12 twist barrels were another winning combination.

Figure out how fast they spin (rpm's = muzzle fps x 720 / twist in inches). Then compare the rpm's they leave at to what a .300 Win. Mag gets as it pushes 'em out at 3100 fps. in a 1:12 twist barrel. Note that for every 100 fps over about 2500 fps, these bullets need to be spun about 2000 rpm faster to stabilize them due to increased air resistance.

I've shot 180 Sierra HPMK's from a 9-pound 26" barreled .300 Win. Mag. with a 1:12.7" twist; great accuracy all the way to 1000 yards. They left about 3100 fps.

January 8, 2013, 01:29 PM	#12
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Bullet stabilization's all about how many rpm's the bullet spins at for a given muzzle velocity. Winchester loads 180's in .308 Win. ammo leaving at 2600 fps in their rifle's 1:12 twist barrels. They're well stabilized. So were the Western Cartridge Company's 197 and 200 grain match bullets made to shoot over 100 fps slower from Win. 70 match rifles chambered for the .308 Win. and 1:12 twist barrels. So were the 180 grain Sierra HPMK's from the Army's M14NM's in competition leaving a bit faster in their 1:12 twist barrels. And they won their share of matches and set a few records with that load. They too, were well stabilized. And the 190 Sierra HPMK's the USN and USAF teams shot from their 7.62 NATO M1's leaving about 2600 fps from their 1:12 twist barrels were another winning combination. Figure out how fast they spin (rpm's = muzzle fps x 720 / twist in inches). Then compare the rpm's they leave at to what a .300 Win. Mag gets as it pushes 'em out at 3100 fps. in a 1:12 twist barrel. Note that for every 100 fps over about 2500 fps, these bullets need to be spun about 2000 rpm faster to stabilize them due to increased air resistance. I've shot 180 Sierra HPMK's from a 9-pound 26" barreled .300 Win. Mag. with a 1:12.7" twist; great accuracy all the way to 1000 yards. They left about 3100 fps. Last edited by Bart B.; January 8, 2013 at 05:33 PM.