Cast and twist rates

[Wolfdog91]

Ok so in general do the same rules that apply for jacked rounds apply for cast? That being you want a slower twist for lighter stuff and a faster for heavier. Or is it something different?

[Harter66]

That has been my experience .
Length is actually the dictation of whether the twist is enough .
Aerodynamics of course play a roll with bullet centers of pressure and gravity .
I have a 222 that is at its best with 50 gr SP , 55s just don't shoot as well 62s were a waste of powder . 62 gr NOE 225-55 shoots as well or better than the 50 gr jackets .
1-12" twist.

I had a 308 that shot extremely well all the way to 175 gr shape made no difference .
1-12" twist .

[bmortell]

ya heaveir dont mean much with cast in that regard. my 220gr cast 30 cals are the same length as nosler 165gr j words, also the center of mass is more in favor to be stabilized easier. same general concept still applies though. the only times ive had stability problems was with 2-4inch barrels.

[charlie b]

The only exception to the 'standard' rule is the upper spin rate. If you have a fast twist barrel then you can spin a cast bullet at too high a rate and it will not fly true.

If you are building a custom rifle for cast then I'd do some research on the bullets you want to use and how fast you want to push them. You may want a slower twist than 'normal' so you can shoot at higher velocities.

[Hick]

What Charlie B said-- in the past some of those who have studied twist rate have recommended that the max spin rate be kept below about 120,000 to 140,000 RPM. For those not familiar with the math, these are the velocities that are around 140,000 rpm for various twist rates:

1:9 1750 fps (CZ-527 ib 223 Rem)
1:9.5 1850 fps (CZ-527 in 7.62x39)
1:9.8 1900 fps (7.65 Argentine Mauser)
1:10 1940 fps (M1 in 30-06, Enfield in 303)
1:12 2330 FPS (Win 94 in 30-30)
1:16 3100 FPS (Win 94 in 32 WS)

hardness and coating also have an effect, so this is only approximate.

[waco]

I shoot the 30xcb in a .308 at over 2600fps in a 1:10 twist with 2moa accuracy out to 500 yards.