twist rate versus bullet weight

rodmkr

Temecula California
Trying to wrap my poor old brain around the statement above.
Working with my Handi Rifle in 223 until the new one arrives.
Looking at several so called experts on the web and none can come to a consensus on cast weight versus twist.
Does anyone have a good if not gold standard for the 223 cast versus twist?
If so what is it or where is it so I can make a copy for my books

Jim
 

rodmkr

Temecula California
Well as I understand it you first need to know the approx. bullet weight
so you can decide on the length of the bullet.
And there are not that many cast 223 bullet molds available.
The only charts I can find are for jacketed bullets and for the 1-9 Handi Rifle it is different on every chart I have seen.
Best so far is the Berger chart which gives a 63 to 70 grain bullet for a 1-9 twist.
In the 63 to 70 grain area there is only one mold that I have and that is the NOE 225-65 grain borerider that lubed and checked with my alloy comes in at 73-75 grains.
The bullet is .074 inches long and sized to 225.
As to chamber throat no test and is not gonna happen that I stick a steel rod down the bore and beat a piece of lead into a case.
Perfect way to completely ruin a rifle bore.

Jim
 

Rick

Moderator
Staff member
While bullet weight often is given as a means to determine a twist rate telebasher is correct, it's the bullet length that's needed to determine what twist is needed. A common method to do this is the Greenhill formula. While it's not an exact science because there can be other factors at play it is usually fairly close and will get you in the ball park.

On this page the Greenhill Formula is explained, you'll notice bullet weight isn't mentioned.

Greenhill Formula

The only correlation to weight is that in a given caliber weight cannot be increased by a larger diameter only by a longer bullet of the same diameter/caliber.

Hope this helps.
 

CZ93X62

Redlands, Kalifornistan
Google "Greenhill Formula Calculator". A cool little program comes up that you plug your data into and provides optimum twist rate
 

Tom

Active Member
Another vote for the Greenhill formula. Higher velocity will let you get away with a longer bullet, within reason.