What would be considered the ideal twist rate for the 357 Mag and the 357 Bain & Davis using 158 to 180 grain bullets in a 20 inch barrel?

Steve E........

Ideal twist rate is usually calculated via Greenhill formula. You can download an app to do the calculation on Z-hat's website.

Find the length of the longest bullet you plan to shoot, and plug it in to the formula with the constant for under 2800 fps (there's a different constant for over 2800 fps).

Most .357's seem to have 1:14 twists, but when I did the calculation based on the Sierra and Hornady 180's (.752 in and .756 in), I came up with 1:25 inches twist. Some Rossi Puma's apparently have 1:30 inch twists good for only 158 gr and below.

HTH,
Steve

1:14" to 1:16". Check out the PPC revolvers' twist.
Regards, Joe

skl1

I had a question of, is that the total length of the bullet or just the bearing surface? I'm thinking from your measurements shown that it is the total length of the bullet.


Steve E.........

Total length.
Also, remember that Greenhill developed his formula to determine the longest bullet that a existing twist could barely stabilize (he was working with existing navel cannons and the (than) new streamlined projectiles).
IOW having a twist rate slightly faster than calculated is not a bad thing.