30 Cal Rifling Twist Rate

[sheepherder]

I was browsing through my old [1970] Lyman reloading manual and noticed the rifling twist for the 30 cal Luger...1 in 9.85" (which works out to 250mm)...

Is that right??? The same manual lists the .32ACP in the Mauser HSC as 1 in 16"; the .38 Super in a 5" Colt as 1 in 16"...

I routinely use Remington Model 700 and Winchester Model 70 rifle barrels in 30-06 for my 30 cal Luger barrels; they are both 1 in 10"...

It seems odd that rifles in 30 caliber should have twists close to the 30 Luger while other ~30 cal pistols use a twist almost twice as long...

I'm not complaining...Just sayin'...

[Schutzenbob]

This is from Wikipedia;

"The common rifling twist rate for 7.65 Parabellum is 275 mm (1 in 10.83 in), 4 grooves, ø lands = 7.62 mm, ø grooves = 7.83 mm, land width = 3.05 mm and the primer type is small pistol."

Which would stabilize a 150 grain bullet. ?quien sabe?

[Sieger]

Originally Posted by Schutzenbob

This is from Wikipedia;

"The common rifling twist rate for 7.65 Parabellum is 275 mm (1 in 10.83 in), 4 grooves, ø lands = 7.62 mm, ø grooves = 7.83 mm, land width = 3.05 mm and the primer type is small pistol."

Which would stabilize a 150 grain bullet. ?quien sabe?

Hi,

Not to be rude or questioning you in anyway, but they are not accurate here at all for an original Luger. Perhaps they got their data from a more modern pistol in this same caliber, as there are quite a few out there.

Sieger

[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

[Schutzenbob]

I think something got lost along the way......I thought the question was about the excessive amount of twist that was used in Luger barrels; a 30 caliber barrel with a pitch of 1-10 inches will happily stabilize a 180 grain bullet.

As an example I plugged the specs from a Lyman/Ideal #311227 lead bullet into the Greenhill Formula to determine the twist necessary to stabilize such a bullet; Diameter .312, Length .538, Approximate velocity 1,200, Material lead/tin. What I got was a pitch of 1 turn in 23 inches. Now.....since luger barrels have about twice the necessary pitch, I have to wonder why? Possibility #1 Did DWM cut down rifle barrel blanks to make the pistol barrels? Possibility #2 DWM's rifling machines were not adjustable and the pitch was set for rifle barrels? Again ?quien sabe?

inputs
bullet length = .538
bullet diameter = .312
muzzle velocity fps = 1,200
bullet SG lead = 11.3

bullet SG values: 11.3 lead
8.9 copper
8.5 brass
7.8 steel

output = 1 turn in 23"





Notes

The classic Greenhill equation is

T' = 150 / L'

where the twist and the bullet length are in calibers. Removing bullet diameter from twist and length gives the equation often found:

T = 150 * D^2 / L

The Greenhill equation includes no term for muzzle velocity, and several sources suggest replacing the 150 with 180 for muzzle velocities over 2800 fps. Increasing muzzle velocity increases bullet spin, and spin provides the stability.

T = 3.5 * V^0.5 * D^2 / L

At 2800 fps, this equation is equivalent to using 185 in the Greenhill equation, and at 1840 fps, this equation is the same as Greenhill's.

[sheepherder]

You got way too much time on your hands, Bob...

[Schutzenbob]

Thank you sheepherder, but it only took a moment.

[Sieger]

Originally Posted by Schutzenbob

I think something got lost along the way......I thought the question was about the excessive amount of twist that was used in Luger barrels; a 30 caliber barrel with a pitch of 1-10 inches will happily stabilize a 180 grain bullet.

As an example I plugged the specs from a Lyman/Ideal #311227 lead bullet into the Greenhill Formula to determine the twist necessary to stabilize such a bullet; Diameter .312, Length .538, Approximate velocity 1,200, Material lead/tin. What I got was a pitch of 1 turn in 23 inches. Now.....since luger barrels have about twice the necessary pitch, I have to wonder why? Possibility #1 Did DWM cut down rifle barrel blanks to make the pistol barrels? Possibility #2 DWM's rifling machines were not adjustable and the pitch was set for rifle barrels? Again ?quien sabe?

inputs
bullet length = .538
bullet diameter = .312
muzzle velocity fps = 1,200
bullet SG lead = 11.3

bullet SG values: 11.3 lead
8.9 copper
8.5 brass
7.8 steel

output = 1 turn in 23"

Notes

The classic Greenhill equation is

T' = 150 / L'

where the twist and the bullet length are in calibers. Removing bullet diameter from twist and length gives the equation often found:

T = 150 * D^2 / L

The Greenhill equation includes no term for muzzle velocity, and several sources suggest replacing the 150 with 180 for muzzle velocities over 2800 fps. Increasing muzzle velocity increases bullet spin, and spin provides the stability.

T = 3.5 * V^0.5 * D^2 / L

At 2800 fps, this equation is equivalent to using 185 in the Greenhill equation, and at 1840 fps, this equation is the same as Greenhill's.

Hi,

Thanks for your post, as I always really appreciate a thorough technical analysis of a given topic!

Let's stop guessing.

Yes, the 7.65x53mm DWM '98s did, indeed, have a twist of 1 in 9.84, 250mm. These shot bullets weighing 154 grains at 2,755 fps.

The original DWM round nose Parabellum bullet was .59055 inches, 15mm, in length, but was not made of lead; rather, it had a lead core and a nickel alloy jacket.

As previously mentioned, the 9mm Luger barrels have exactly the same twist.

Over-spun or not, when loaded to original DWM specs, both the 7.65mm and 9mm Parabellums can be incredibly accurate cartridges when shot through Lugers.

Whatever the case regarding the adjustability of their rifling machinery, DWM produced some excellent quality pistols that shot quite accurately.

It may mean something that over-spun bullets have better terminal affect when creating wound channels.


Sieger

[Paladinpainter]

Sieger,
I'm going to jump in here and question the notion that an over-spun bullet has a different terminal effect than a normally spun bullet. If the target is 10" thick, a bullet leaving a 1 in 9.84" twist barrel, will rotate about one time before it exits. ( Not tumbling). A bullet leaving a 1 in 20" twist barrel will rotate about half that amount. In either case, and with out testing, I have a hard time believing that one half a rotation of the projectile is significant in any way. Now if the projectile upsets on entry, that might be different. But we're still talking about 1 rotation in each 10 inches of travel.
Regards,
John

[Sieger]

Originally Posted by Paladinpainter

Sieger,
I'm going to jump in here and question the notion that an over-spun bullet has a different terminal effect than a normally spun bullet. If the target is 10" thick, a bullet leaving a 1 in 9.84" twist barrel, will rotate about one time before it exits. ( Not tumbling). A bullet leaving a 1 in 20" twist barrel will rotate about half that amount. In either case, and with out testing, I have a hard time believing that one half a rotation of the projectile is significant in any way. Now if the projectile upsets on entry, that might be different. But we're still talking about 1 rotation in each 10 inches of travel.
Regards,
John

John,

There are several good articles on the net regarding the factors improving terminal effect in meat. Bullet rotation is one of them.

Frankly, with only a 93 grain FMJ bullet, either round nose or truncated cone, I'm inclined to agree with your basic proposition.

Sieger

[Sieger]

Originally Posted by Rick W.

14 Walker

56 Sieger