I would agree to the extent that a gain-twist barrel CAN give accuracy comparable to fixed-pitch barrels, but would note that, for reasons mentioned earlier, it is more difficult to make a really excellent gain-twist barrel than a fixed-pitch one, or to achieve top accuracy from one because the gain-pitch is harder on the bullet's geometry as delivered at the muzzle.
I will caveat these statements, too, as applicable to elongated projectiles, specifically - I am not at all sure that a patched roundball is sensitive to changes in pitch to the same extent, or would suffer much from slight slowing at or near the muzzle, so long as the resulting rotational speed is sufficient to stabilize the ball.
It may also be of interest to note that button-rifled barrels, long noted for excellent internal finish (when properly made), and top-level accuracy (if made by one of best makers, such as Shilen), WILL exhibit small variations in pitch from end-to-end. That is because the rotation of the button on its passage through the bore is affected by variations in hardness of the barrel material (unavoidable), and the fact that the forces on the button and the barrel steel are so great that there is no way to effectively control its rotation to prevent such minor deviations. In spite of this, excellent barrels are made by button-rifling, and match winning rifles assembled with them.
mhb - MIke
