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Old September 9, 2020, 09:33 AM   #8
Senior Member
Join Date: March 18, 2009
Location: Temple, TX
Posts: 793
@ Wallyl:
I used the Miller Gyroscopic stability factor formula (below) to check the twist, where

S = gyroscopic stability factor (dimensionless)
W = bullet weight (grains)
T = twist (inches per turn)
L = bullet length (inches), for plastic tipped bullets, ignore length of plastic tip
D = bullet diameter (inches)

S= [30*W*D(exp2)] / {(T)exp2*L*[(D)exp2 +(L)exp2]}

"S" should be between 1.3 and 2.0. Best range is between 1.4 and 1.7.

The formula is not as daunting as it looks. I couldn't figure out how to do superscripts, and so (T)exp2 means T squared. I used a bullet length of 1.06 inches for the 105 grain A-max and calculated an "S" of 1.73 for your parameters. So, the 105 A-max should stabilize. But these things are never precise and every gun is different.

During my fifty years of shooting, I've had at least six .243's come and go, and still have two more in the safe. It seemed like none of them did their best with bullets in the 100 to 105 grain range. For deer hunting, I used a 95 grain nosler partition, and it worked fine. I hear, a lot, that the .243 Win is inherently accurate, but I never found that to be the case. Each rifle was bug hole accurate with one specific bullet weight and one particular powder, but it was never the same from rifle to rifle. I spent a lot of different powders and different bullets trying to fine that magic load, and it got frustrating pretty quickly.

@mxsailor: I noted that you have a remington 788. Of all the .243's I've owned, my 788 was the most accurate. Unfortunately, it got stolen about 40 years ago.

Last edited by hammie; September 10, 2020 at 05:49 PM.
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