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Twist rates

12 Jun 2023
@ 08:18 pm (GMT)

Andrew Murray

G'day all,

Has anyone encountered reading on slowing the twist down, or potentially speeding it up, to increase the effectiveness of copper solids?

Slowing it down causing a tumbling effect or to speed it up causing an inordinate amount of rotational stress that upon impact it essentially crumbles/breaks to pieces?


13 Jun 2023
@ 07:31 am (GMT)

Nathan Foster

Re: Twist rates
Hi Andrew, I discussed this in the second edition of the book, Long Range Rifles.

Increasing twist does not cause homogenous copper to break to pieces, though it can encourage petals (one or more) to break away. It is not however a reliable method of action - the material is poor to begin within. A fast twist does however help to stabilize copper.

The use of a slow twist is also problematic. In order to have the bullet unstable on impact, it will not be fully stable in flight. In other words, the rifle will not produce optimum accuracy. Furthermore, the tumbling action is not wholly reliable. Again, this is the wort of thing that one can perhaps exploit when encountered, but it is perhaps not a good idea to deliberately set up a rifle for this purpose.

I suppose one could try to enhance slow twist tumbling as per .303 ball ammo by utilizing an extremely light weight ogive. The effect in the .303 was never consistent but such a load could perhaps be made more effective within an expanding bullet (perhaps utilize the plastic tip design from the Winchester Extreme Point). Quite possible but again, the slow twist is an issue with regards to accuracy.

As a mode of action, tumbling does allow a bullet to offload kinetic energy. But in order to maximize the effect, velocity needs to be relatively high (hydraulic force). Mechanical wounding / direct force is also quite vivid though again in the absence of velocity, the wound is proportionate to the length (rather than diameter) of the bullet.

13 Jun 2023
@ 11:03 am (GMT)

Andrew Murray

Re: Twist rates
It is unfortunate, in that I foresee lead being banned in projectiles before too long, there are states in Australia that have already banned lead shot and lead in rifle projectiles is not far away. Perhaps the long-range hunting projectile with it.

On another note, shooters here do themselves no favours when it comes to advocating for the ownership and use of firearms. There are no real coherent efforts or plans to ensure the future of the sport, let alone what kind of projectiles we can use.

I watched a video of a Sherman tank firing in slow-motion, the amount of yaw in the projectile was phenomenal. Perplexing how such a projectile would penetrate armour at all given that it was essentially see-sawing through the air.

13 Jun 2023
@ 06:16 pm (GMT)

Scott Struif

Re: Twist rates
Hi Andrew. There’s US company that sells copper bullets designed to tumble on impact.


We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.