[Danny1203]

Have heard the twist rate of a barrel can affect the pressure. First off is this true or false? Secondly would be, if It does affect the pressure how or why would that cause the pressure to be affect? New to this topic and wasn't sure how exactly it worked. Thanks in advance!

[oneineight]

First, I have not tested the results.
But a faster twist rate will make the path the bullet follows down the barrel longer.
I have heard others mention that twist rate can be a factor in pressure.
When reloading, it's nice to leave a margin of error in the pressure levels.

[Propagandalf]

I believe you choose twist based on length/weight of the bullet needing to be stabilized. The length of the throat for pressure. I.E. longer throat in 5.56 vs. .223 and faster twist for each as bullet grain increases.

[twobobbwana]

Greenhills formula is what you need. Bullet Weight/Length and velocity must be considered.

Usually long/heavy bullets use a tighter twist rate than light/short bullets...............then velocity must be considered