Originally Posted by Kronberg
The barrel length thus influences the needed spin through the increased velocitiy. The 1-11 twist near the crown of a 26" barrel will spin the bullet accordingly a little bit faster than the one near the crown of a 20" one.
Did one of the members here experience an sudden opening up of a group of heavy (long) bullets shot out of a barrel with relative low twist at a longer range compared to range shorter by 50-100 yards?
In response to your first comment yes. But only in the sense that the increased velocity is due to the longer barrel. All else being equal such as equal velocity and equal twist regardless if it was fired from a 17" barrel or a 30" barrel the stability factor will be identical or scary near identical.
The second comment or question is not that simple. You can have a negative impact on downrange accuracy from both a bullet with a very low stability factor or a very high one. That statement is made through experience and is NOT scientifically NOR mathematically based so take it with a grain of salt. As MikeCr brought out, if a bullet doesnt hit the target sideways at 50 or 100 yards, it is stable be it marginal (low SF) or perfect (optimum SF) or otherwise (high SF). Regardless, it is gyroscopically stable. Which spectrum of SF a bullet is in can affect close, mid point and long range accuracy yes.
Not sure if that answers your questions.