In 1892 the Army switched from the .45-70 Trapdoor Springfield Rifle to the .30-40 Krag-Jorgensen and there was much rejoicing. The .30-40 Krag was load with a 220 grain jacketed lead round nose bullet fired at around 2000 fps. This bullet required a 1 in 10 inch twist to stabilize this built. During the Spanish-American War in 1898 the .30-40 Krag cartridge and Krag-Jorgensen Rifle that fired proved less effective the Spanish Mauser and 7mm Mauser that was used against them.
So, back to the drawing bored again and the 1903 Springfield Rifle and the .30-03 cartridge to fired from it were born. The .30-03 kept the 220 grain bullet (and the 1-10 twist) but increased the velocity to about 2100 fps. About this time every other country in the world was implementing lighter, faster spitzer type bullets that were more accurate at longer ranges.
Back to the drawing board again for the .30-06. A 150 Grain bullet traveling at 2750 FPS was decided upon. And the cartridge renamed .30-06 At the time all of the tooling and all of the machines used to make rifle barrels were set-up for the 1-10 twist. Since the testing was conducted in a relatively short period time and tooling was extremely expensive at the 1-10 twist was retained. In actuality, a 1-14 Twist barrel is sufficient to stabilize the 150 grain bullet at that velocity. While the 1-10 twist is over-stabilizing the 150 grain bullet, accuracy was still “good enough for government work” and delivered under the 3” at 100 yards requirement. Also, it is a thick Full-metal jacket bullet, so there was no fear of jacket failure due to excess RPM.
On the commercial front, as gun manufacturers started to produce rifles and ammunition for the .30-06, the used the 1-10 twist because they had the tooling and accuracy was sufficient. Also several manufacturers continued to load the 220 grain bullets for hunting large and dangerous game which requires the 1-10 twist. So, commercial manufacturers use the 1-10 twist in .30-06.
After WWII and further reinforced during the Korean Conflict, The powers that be decided that they needed, reduced recoil and more “Firepower” and decided to switch to the M14 and the 7.62 x 51mm NATO and 147 Grain bullets. Again, the tooling available was mostly geared for the 1-10 twist and again it was good enough for Government work. It was not until the National Match teams started playing with the M14 did things change. First, the adoption of the best target bullet, at the time, was adopted, the 168 Sierra Match King. Second, Lake City NM Brass was made available and the M852 Match ammo was born. Third, a proper chamber was designed. And lastly, a better twist rate was chosen, the 1-12.0. In most circumstances a 1-13 would have been sufficient, but the 1-12 provides a little bit of insurance. Later on when the M852 was dropped in favor of the M118LR with the 175 grain Sierra Match King (which can stay supersonic to longer ranges than the 168 because of higher ballistic co-efficient), the 1-12.0 twist remained because it can actually stabilize a 185 grain bullet in most circumstances.
So why were most factory .308 Winchester guns still using a 1-10.0 twist? That's what they were still geared up for in .30 caliber production and accuracy was factory acceptable. This also why all .300 win mags are also a 1-10 twist.
So, where the hell did the 1-11.25 twist come from and why? Once upon a time the Military asked a well known barrel maker to make some barrels for them. They specified a 1-12.0 Twist. This barrel maker informed them that he did not have a gear for his machine that would make a 1-12.0. He could make a 1-11.25 twist or a 1-13.0 twist. They chose the 1-11.25 (faster is always better for the Military, see the 62 grain 5.56 bullet in a 1-7.0 twist barrel). The barrels shot much better than the barrels that they had been using, so on all future orders they listed a 1-11.25 twist and through the magic of red tape this became a requirement.
So, back to the drawing bored again and the 1903 Springfield Rifle and the .30-03 cartridge to fired from it were born. The .30-03 kept the 220 grain bullet (and the 1-10 twist) but increased the velocity to about 2100 fps. About this time every other country in the world was implementing lighter, faster spitzer type bullets that were more accurate at longer ranges.
Back to the drawing board again for the .30-06. A 150 Grain bullet traveling at 2750 FPS was decided upon. And the cartridge renamed .30-06 At the time all of the tooling and all of the machines used to make rifle barrels were set-up for the 1-10 twist. Since the testing was conducted in a relatively short period time and tooling was extremely expensive at the 1-10 twist was retained. In actuality, a 1-14 Twist barrel is sufficient to stabilize the 150 grain bullet at that velocity. While the 1-10 twist is over-stabilizing the 150 grain bullet, accuracy was still “good enough for government work” and delivered under the 3” at 100 yards requirement. Also, it is a thick Full-metal jacket bullet, so there was no fear of jacket failure due to excess RPM.
On the commercial front, as gun manufacturers started to produce rifles and ammunition for the .30-06, the used the 1-10 twist because they had the tooling and accuracy was sufficient. Also several manufacturers continued to load the 220 grain bullets for hunting large and dangerous game which requires the 1-10 twist. So, commercial manufacturers use the 1-10 twist in .30-06.
After WWII and further reinforced during the Korean Conflict, The powers that be decided that they needed, reduced recoil and more “Firepower” and decided to switch to the M14 and the 7.62 x 51mm NATO and 147 Grain bullets. Again, the tooling available was mostly geared for the 1-10 twist and again it was good enough for Government work. It was not until the National Match teams started playing with the M14 did things change. First, the adoption of the best target bullet, at the time, was adopted, the 168 Sierra Match King. Second, Lake City NM Brass was made available and the M852 Match ammo was born. Third, a proper chamber was designed. And lastly, a better twist rate was chosen, the 1-12.0. In most circumstances a 1-13 would have been sufficient, but the 1-12 provides a little bit of insurance. Later on when the M852 was dropped in favor of the M118LR with the 175 grain Sierra Match King (which can stay supersonic to longer ranges than the 168 because of higher ballistic co-efficient), the 1-12.0 twist remained because it can actually stabilize a 185 grain bullet in most circumstances.
So why were most factory .308 Winchester guns still using a 1-10.0 twist? That's what they were still geared up for in .30 caliber production and accuracy was factory acceptable. This also why all .300 win mags are also a 1-10 twist.
So, where the hell did the 1-11.25 twist come from and why? Once upon a time the Military asked a well known barrel maker to make some barrels for them. They specified a 1-12.0 Twist. This barrel maker informed them that he did not have a gear for his machine that would make a 1-12.0. He could make a 1-11.25 twist or a 1-13.0 twist. They chose the 1-11.25 (faster is always better for the Military, see the 62 grain 5.56 bullet in a 1-7.0 twist barrel). The barrels shot much better than the barrels that they had been using, so on all future orders they listed a 1-11.25 twist and through the magic of red tape this became a requirement.
