twist rates for low velocity

[robbor]

When selecting a twist rate for a subsonic or low velocity round how should you adjust the twist rate? Im guessing go 1-2" more twist? thinking of like a 6.5 wisper or something.

 

[Steve Blair]

This article has a link to download Don Miller's formulas in Excel spreadsheet form. It can help you to predict bullet stability variation by velocity, twist and temperature.

Generally, the twist must be increased as velocity decreases. It may not be as much as you think.

 

[canderson]

robbor,
You are pretty close. I have a friend with a 300 whisper 1-8 twist. He can shoot the 220's fine, but the 240's will not fully stabilize. He is also using the Miller formula to determine the twist for a 6.5 subsonic round. I will try to contact him to find out what he concluded.