Thoughts on ideal twist rates for big bore 357 & 457 for slug use

[Airgun-hobbyist]

Can we get a discussion going on optimum twist rates for big bores... A bit of information is needed to order a few barrel blanks in different calibers (with the optimal twist rates) from TJ's. Because we are dealing with heavier slugs, both cast and swaged, (not pellets) what would be the ideal twist rate nowadays given the higher pressures and speeds up around 950 fps for both a 357 and a 457?

TJ's offer a decent amount of options in rifle barrel liners for the 457 twist rate (getting a 45-70 liner), and only two options in 357 twist rates (one being an airgun liner), as does Lothar-Walther. There are also other barrel blank manufacturers that make match grade barrels, but have twist rates around 1-14" that may work. So what is the general consensus?

 

[MickeyD]

It depends on the round, specifically the length, weight and actual diameter, and the muzzle velocity. Ideally you want a twist that will give you a Gyroscopic Stability figure of 1.5 or so. There are several web sites that provide calculators to help figure this out.

For example, one Nielson 357 round weighs 178 grains and is 0.82 inch long. With the 1/26 twist barrel, the figure will be 1.2. This is borderline, the bullet could tumble in certain conditions. However, the 1/16 liner would give figure of 3.17. This is way over-stabilized. The slugs gyroscopic action will tend to keep the slug pointed upwards when it should be tipping down as the slug passes maximum rise.

 

[RM.510bigbore]

On JBM ballistics there is a twist rate calculator .That will satisfy any twist need. For for thought 45 acp shoot same bullets at basically same speed as are .457 Texans and they use a 16 twist . Been working for a long time.