30 Cal Rifling Twist Rate

Sieger · 02-21-2015, 04:28 AM

Hi,

Well, here is what the Pre-WWI DWM Owner's Manual says:

Twist, 9.84 inches (exactly the same as the 9mm), 250mm.

Depth of grooves, .005 inches, 0.125mm

Width of lands, .122 inches, 3.1mm

Diameter of grooves, .311 inches, 7.9mm

Their metric numbers are perfect, with only slight rounding used for their inch numbers.

Please note that the Lyman Handloading Manual (above) groove diameter is way off. Stranger yet, please know that several of the original DWM bullets I've measured were all at .309 diameter.

Why shoot a .309 bullet down a .311 barrel? In the 9mm, why shoot a .355 bullet down a .358 barrel?

I hope this helps.

Sieger

02-21-2015, 04:28 AM	#4
Sieger User Join Date: Jul 2003 Location: New York, NY Posts: 1,579 Thanks: 2,154 Thanked 402 Times in 251 Posts	Hi, Well, here is what the Pre-WWI DWM Owner's Manual says: Twist, 9.84 inches (exactly the same as the 9mm), 250mm. Depth of grooves, .005 inches, 0.125mm Width of lands, .122 inches, 3.1mm Diameter of grooves, .311 inches, 7.9mm Their metric numbers are perfect, with only slight rounding used for their inch numbers. Please note that the Lyman Handloading Manual (above) groove diameter is way off. Stranger yet, please know that several of the original DWM bullets I've measured were all at .309 diameter. Why shoot a .309 bullet down a .311 barrel? In the 9mm, why shoot a .355 bullet down a .358 barrel? I hope this helps. Sieger Last edited by Sieger; 03-02-2015 at 04:29 AM.

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