The Firing Line Forums - View Single Post - Experience shooting 175gr .308 out of 1:12 twist??

Bart B. · March 5, 2013, 12:51 PM

1:12 twists have been used with great success for the .308 in competition. Both the military's M14 and M1 rifles chambered for it had standard barrel twists at 1:12. Bullets from 150 to 180 grains won matches and set records from both. Only the M1 and its 24 inch barrel did well with 190's; the 22 inch tube in M14's wasn't quite long enough to get enough muzzle velocity to spin 190's fast enough to keep 'em stable to 1000 yards.

In warmer weather, i.e. above 70 deg. F, a muzzle velocity of 2500 fps will stabilize a Sierra 175 HPMK well enough from a 1:12 twist barrel in elevations above 2000 feet. Cooler weather and/or lower elevations will need a 1:11 twist at that exit velocity. The arsenal loaded 175 HPMK's leave 22 inch barrels at about 2600 fps; about 2550 fps at 26 yards where the arsenal chronograph measures their speed.

Note that the 7.62 NATO and .308 Win. rounds were both developed with 1:12 twist barrels and that's what Springfield Armory (in MA) and Winchester barrels had. Bullets from 150 to 200 grains were tested with that twist and all did great; the 200-gr. ones by Winchester were good enough for hunting use up to 200 yards which is what they were meant for to begin with.

For what it's worth, I don't think any powder will produce the accuracy for 175's in a .308 case that IMR4064 will. That case with that powder's shot test groups with 168 through 190 grain bullets smaller than or equal to current benchrest records. But you gotta weigh each charge; it don't meter too accurate.

Yes, it takes max loads to push a 175 out of a 24" barrel at 2600 fps. More than max to get that out of a shorter barrel unless one uses one of the super powders now on the market. But how accurate will one of those super powders shoot them?

March 5, 2013, 12:51 PM	#7
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	1:12 twists have been used with great success for the .308 in competition. Both the military's M14 and M1 rifles chambered for it had standard barrel twists at 1:12. Bullets from 150 to 180 grains won matches and set records from both. Only the M1 and its 24 inch barrel did well with 190's; the 22 inch tube in M14's wasn't quite long enough to get enough muzzle velocity to spin 190's fast enough to keep 'em stable to 1000 yards. In warmer weather, i.e. above 70 deg. F, a muzzle velocity of 2500 fps will stabilize a Sierra 175 HPMK well enough from a 1:12 twist barrel in elevations above 2000 feet. Cooler weather and/or lower elevations will need a 1:11 twist at that exit velocity. The arsenal loaded 175 HPMK's leave 22 inch barrels at about 2600 fps; about 2550 fps at 26 yards where the arsenal chronograph measures their speed. Note that the 7.62 NATO and .308 Win. rounds were both developed with 1:12 twist barrels and that's what Springfield Armory (in MA) and Winchester barrels had. Bullets from 150 to 200 grains were tested with that twist and all did great; the 200-gr. ones by Winchester were good enough for hunting use up to 200 yards which is what they were meant for to begin with. For what it's worth, I don't think any powder will produce the accuracy for 175's in a .308 case that IMR4064 will. That case with that powder's shot test groups with 168 through 190 grain bullets smaller than or equal to current benchrest records. But you gotta weigh each charge; it don't meter too accurate. Yes, it takes max loads to push a 175 out of a 24" barrel at 2600 fps. More than max to get that out of a shorter barrel unless one uses one of the super powders now on the market. But how accurate will one of those super powders shoot them? Last edited by Bart B.; March 5, 2013 at 01:05 PM.