THE AMOUNT OF TWIST IN THE RIFLE BARREL
A rifle bullet is much like a top. It has to be spun at a certain rate of speed in order to remain stable and
point on. Spin the top too fast and at first it wobbles, before it settles down to a smooth spin. Then as its
speed of rotation diminishes, it finally begins to wobble once more. The forward velocity of a bullet,
however, diminishes more rapidly than its rotational speed.
The longer the bullet and the slower it leaves the muzzle, the faster the pitch of the rifling must be in order
to keep the bullet point on and accurate. Short bullets like the 30-30 Win. which weighs 150 grains, can
be stabilized in a twist having one turn in 12 inches. In other words, 1-12. The twists in barrels
chambered for the old black powder cartridges, that used bullets that were relatively short in proportion
to their diameter, were quite slow. The standard twist for the .45/70, for example, was 1-20. The twist for
the Winchester .50/95 was 1-60 and for the .50/1 10 1-54.
Here is a list of finish sizes of the sizing button, the rifling button, and the degree of angle to get the twist
that is listed.
RIFLE BARREL TWIST
CALIBER MAKE BORE GROOVE TWIST
DIA. DIA
.30 WCF (30-30) Winchester .300 .308 12"
.30 Remington Remington .300 .308 12"
.30 US (30-40) Springfield Armory .300 .3085 10"
.30-06 Springfield Armory .300 .308 10"
.30 Newton Newton .300 .309 10"