ORIGINAL: yeoman
I admit to a bit of confusion regarding twist rates. For instance, if a 1:70 is good for a roundball, why isn't a 1:48 even better? If a 1:24 is good for a sabot, why not a 1:12 even better? Clearly, there may be a point at which you simply can not get an object to rotate in such a short span under the desired powder charge. Maybe that barrier is the 1:21 found in carbines. Apparently so, for sabots. Maybe the 1:21 is optimal for sabots, a 1:28 for conicals and 1:70 for PRB. I suspect as much. Just wondering why there isn't a pretty darn accurate table where you could look up virtually any bullet on the market, match it up with a given powder/charge, and get the optimal twist rate for delivering it accurately.
There are two things that enter into an answer,we will work with the round ball first, understand that the PRB is using a cloth patch; to fast a twist affects how hard you can push the combination with out "blowing" the patch. Thats why the max hunting load of a 1-48 will be less than a 1-70. The other thing that plays a big part in the twist is stabilization for an example we look to a gryroscope which will hold its position if spun at the right speed for its length and diameter. The same applies to the twist in a rifle barrel. The speed of the bullet going down the barrel together with the twist control how fast the bullet spins when it is the right length and diameter going down the barrel at the right speed it becomes stable which is what you need to put them in the same hole at any distance. I would also point out that just a little to slow and the bullet wobbles this immedately destroys accuracy; a bit fast on the other hand will only graduly affect accuracywhen it starts to vibrate then they start wandering of course.
Hope this helps. Lee