30 Cal Rifling Twist Rate

[Sieger]

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

[sheepherder]

As far as Wikipedia goes, I accept their articles with the same skepticism as I would the writing on the men's room wall at my favorite bar. Any moron can post to Wikipedia, and usually does.

I like to gather 5 or 6 articles from the Net, with visibly different sources [pics, descriptions, dimensions etc] and take an 'average' of them all for my own uses. Of course, if it is in Machinery's Handbook, then it is gospel handed down from Heaven above, and should be treated as such.

In my own experience, the land diameter of my Luger 7.65mm barrels is right at 7.65mm [.301"]. I use a 7.6mm squib rod as reinforcement for my mount/dismount procedures. The .05mm [~.002"] makes it too tight for my preference. .301" + (2 x .005") [assumed groove depth] = .311". That's kind of high, IMO, for a 30 cal bullet - I'd assume .004" groove depth, which gives .309", pretty close to what bullet mfg's quote their "30 cal" bullet size as.

The 8.82mm land diameter found on most P08 barrels works out to .347". If you assume .005" groove depth, that gives you .357"...Again, IMO, kind of high...I'd assume .004" again, which gives .355"...A common "9mm" bullet size...

Just an observation; nothing pertinent to this thread.

[Sieger]

Originally Posted by sheepherder

As far as Wikipedia goes, I accept their articles with the same skepticism as I would the writing on the men's room wall at my favorite bar. Any moron can post to Wikipedia, and usually does.

I like to gather 5 or 6 articles from the Net, with visibly different sources [pics, descriptions, dimensions etc] and take an 'average' of them all for my own uses. Of course, if it is in Machinery's Handbook, then it is gospel handed down from Heaven above, and should be treated as such.

In my own experience, the land diameter of my Luger 7.65mm barrels is right at 7.65mm [.301"]. I use a 7.6mm squib rod as reinforcement for my mount/dismount procedures. The .05mm [~.002"] makes it too tight for my preference. .301" + (2 x .005") [assumed groove depth] = .311". That's kind of high, IMO, for a 30 cal bullet - I'd assume .004" groove depth, which gives .309", pretty close to what bullet mfg's quote their "30 cal" bullet size as.

The 8.82mm land diameter found on most P08 barrels works out to .347". If you assume .005" groove depth, that gives you .357"...Again, IMO, kind of high...I'd assume .004" again, which gives .355"...A common "9mm" bullet size...

Just an observation; nothing pertinent to this thread.

Hi,

I wouldn't assume anything, but rather would take the DWM Owner's Manual's, and the original drawings' figures as the Gospel as handed down from Georg Luger himself!!!

Ha!!!

The 7.65 Luger and 7.65x53mm DWM '98 Mauser Rifle barrels are both at .311 groove diameter, not .309.

Again, a great mystery to me is why they designed their Parabellum ammo to shoot .309 bullets through .311 barrels; whereas, original 7.65x53mm rifle bullets I've examined were just at .311 diameter.

As to the 9mm, the in spec. groove diameter is 9.1mm (plus 0.01, minus 0.03). At a conversion ratio of .03937, the groove diameter of a 9mm is .358267, if it is in spec.

I hope this helps.


Sieger