from the old forum:
Could someone explain the effect of the twist rate calculation? If one were to make a bullet for a gun with a 1 in 16" twist, should the bullet be designed so that the suggested twist ends up as 1 in 16" or what?
Thanks. As you can tell, I'm confused.
** So many people get confused by the "suggested twist" that I am tempted to delete it from the program.
The "suggested twist" is my best guess at the ideal twist for a given bullet. If you were going to buy a custom barrel just for a particular bullet, you should consider the "suggested twist." Otherwise, don't worry about it. It is not a minimum twist nor a mandatory twist.
Most factory barrels do not have a twist that is ideal for our cast bullets. It seems like the twist is usually too fast, and occasionally too slow, but never just right. We learn to live with it, just like all the other factory imperfections that we learn to live with.
For example, most 357 magnums have a 1-16 twist which would be perfect for a 250 grain bullet, but who shoots a 250 grain bullet in a 357 magnum? The 1-16 twist makes our cast bullets work harder than they need to.
The jacketed crowd will say that it doesn't hurt to overstabilize a bullet but that is not true for cast bullets, because soft lead bullets are easily damaged by the high rotational acceleration forces. Furthermore, almost all cast bullets will be imperfectly balanced to some degree, and when you spin an imperfectly balanced bullet, the spin makes it try to wobble. The faster you spin it, the more it tries to wobble. We don't want our cast bullets to spin any faster than necessary.
However, unless you are going to buy a custom barrel, there is nothing you can do about the twist in factory barrels, so just don't worry about it.
As soon as I win the lottery, I will replace the 1-16" factory barrel on my Marlin 357 with a 1-20" or 1-22" barrel, which would be a little gentler on 180 gr. bullets. In the meantime, there is not much I can do about the factory barrel, and I'm sure not going to switch to a 250 gr. bullet just to be more compatible with the twist.