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Old September 23, 2020, 01:27 PM   #14
Jim Watson
Senior Member
 
Join Date: October 25, 2001
Location: Alabama
Posts: 18,486
I plugged in the values for .30 Luger and got a stability factor of 6.
A lot of Service Pistol and USPSA Open guns are getting 32 twist barrels for a 9mm stability factor in the 1.5 range like a rifle.

Back in the days of the 1903 Springfield, they machine rest tested .30 rifles, spot check on service rifles, all Sporter, NM, and Free rifles.
There is a legend that one month they noticed that accuracy was better and they wondered why. Checking back, they found that the machinist setting up the rifling machines had used the wrong sine bar and turned out a number of barrels with 11 twist. So what did they do? Revise the spec? No, they readjusted the rifling machines for the standard 10 twist.

Last edited by Jim Watson; September 23, 2020 at 01:39 PM.
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