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View Full Version : Need formula for twist vs bullet weight


mugsie
10-16-2011, 08:46 PM
Does anyone have a formula for calculating optimal bullet weight for a specific twist barrel? Caliber has to be factored in as well I'm sure. I'm tyring to optomize a 260 Rem in 1:8 twist, Ranges will be 100 - 300 yards max. Thanks.
seanhagerty
10-16-2011, 09:00 PM
http://kwk.us/twist.html
MrMajestic
10-16-2011, 10:59 PM
Diameter, weight, length, velocity, temperature, pressure and twist. Below is the Miller formula which is a bit more refined then the Greenhill. As far as optimizing the weight it is the heaviest(along with accompanying Ballistic Coefficient) you can stabilize for long range shooting.
http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
mugsie
10-17-2011, 06:46 AM
The reason I ask, is I usually shoot 69g BTHP's out of my 223. They typically shoot 3/4 to 1 moa. Some times a little better, but typically 3/4 MOA. The other day I loaded up some 55g Nosler Spitzers which someone gave me. These were consistantly shooting 4 and 5 hole groupe virtually one hole. I was amazed sinze my rifle is a 12 BVSS in 1:9 twist. I always thought the 69 grainers would be more stable - surprise! Now I'm looking to go out to purchase more 55 grainers. BTW - the 55's were shot with mixed range pick up brass too!
MrMajestic
10-17-2011, 09:04 PM
Don't confuse accuracy with stabilization. I seriously doubt that with a 1in9" twist that any 69 grain bullet would be unstable. Take a walk on the wild side and try some 75 grain A-Max! That's were long range bullets in the .224 bore start.
Jamie
10-24-2011, 08:24 AM
Don't confuse accuracy with stabilization. I seriously doubt that with a 1in9" twist that any 69 grain bullet would be unstable.

Exactly. You can find a formula for what twist you need to stabilize a bullet but only your barrel will tell you what is the optimal bullet for it. As I have tstated before twist rate is only relative to stabilizing the bullet. It does not mean that a 1:8 twist 6.5 will love 142 grain bullets. I have a Rock River AR with a 1:8 twist that will shoot 10, 55 grainers into 1" but won't put 3, 75 grain Amaxes anywhere close to each other.