Determining optimal rifle twist using the Greenhill formula.

[Sharpie443]

I got a question from someone on youtube asking why rifling and bullets in general haven't changed much over the years. His message boiled down to him wanting to know why we don't try to make better rifling to improve accuracy. Obviously there are a number of things wrong with his question but I don't think a lot of new shooters understand rifling or how we determine what twist will gyroscopically stabilize a round.

So I made a video explaining the Greenhill formula and how we determine what twist to use with different projectiles. I also talked about needing a faster twist with subsonic and things like that.

I figured someone here might be interested in it. The video involves math so I’m not sure how popular it will be.

http://www.youtube.com/watch?v=4WKztzgcnQw&list=UU_i0O7tE8cUH0CTk3VqtM6w&index=1&feature=plcp

 

[Jim Watson]

My question would be, why does he THINK we don't?
He is obviously not well informed.
There have been a lot of developments just over my shooting career.

The Greenhill Formula of 1879 is not one of them. There are better ways that take into account actual bullet stability and more aerodynamic shapes than Sir George knew of.

 

[Sharpie443]

Yes that is very true but the Greenhill formula is the most simplistic and easy to explane. It was originally intended for rifled artillery but it works if you just want to explane twist. I would like to do a video on the evolution of cartage design someday when I have time.

 

[Fishslayer]

Interesting. I've been on a Mosin kick lately & kind of shake my head at the variety of milsurp projectiles available. 147gr light ball with lead core and steel core, 174gr heavy ball lead... I believe their match/sniper ammo was 180gr lead core... Then you have the short barrelled carbines. I've pretty much just been trying different stuff & seeing what works.

Of course, Comrad Zaitsev & his students notwithstanding, precision marksmanship didn't seem to be a big part of the Russian philosophy...