Dear Mr. Moeller,
Thank you for your work and great articles, but a lot of "better" ones are in German which unfortunately I don't understand (one article about Muendungsbremse comes to mind). There are a few things I want to ask if you don't mind:
OK, thank you very much for your time, Mr. Moeller, and sorry for the
Hans Adhitya , Sonntag, 11. Dezember 2005 04:23
Yes! Progressive Rifling means, the Barrel start with a
not so steep Twist angle, may half of the final one, and only further down
the Barrel the Twist steepens to the final Angle. If You like this the be
explained in Twist length, the same would mean, the Twist near the Chamber
is long and then shortens towards the Muzzle. Look at the Chamber pressure
over Bullet travel above and You will see, the highest Pressure occurs
relatively close to the Chamber. Pressure und Twist angle determine the
Torque on the Bullet, and hence the needed Drive band strength. While one
cannot change the Pressure a lot (only slightly by loading certain Powders
with specific Burn rates and Form factors) , the Twist angle indeed can be
changed. The Idea behind a progressive Twist barrel is to decouple the
highest Pressure from the steepest Twist. If the full Twist angle for
instance only starts 600 mm down the Barrel the Pressure is only 963 bar,
compared to 4835 bar max. Pressure, or 20% (on fifth). The Drive bands
encounter under such Condition only 20% Sheer force, compared to a
The Benefit of such comparably thin and fragile Structures is, the Engraving force and Friction shrink along. That was the original Motivation for Drive bands anyway. The Effect has been measured an proofed.
The additional Advantage encounters the Shooter, not the Bullet. While shooting the Rifle will spin much less around the Barrel Axis. Together with a well adapted Muzzle Recoil brake or a Silcencer and Flash hider, that incorporates such gas dynamic Recoil brake, the Shooter may actually see through his Rifle scope, where the Bullet hits (if not too far away). Conventional Rifles move the Scope so much, that the Shooter usually cannot keep Sight on the Target while shooting, because the Recoil moves the Scope back and out of Focus and the Bullet torque spins the Rifle to move teh Scope sideways, so, unless the Parallaxe adjustment is perfect, the Off-Center-View blurs.
This is a great advantage, becaus no only the Spotter but also the Shooter can watch the Shot's Effect on the Target. As You know, 4 Eyes see more than 2! So the gathered Information is of greater Reliability.
Ask Walther. Maybe they tell You the Button rifling
Process. In Principle Walther presses a certain shaped Mandrill (Button)
through the bored and honed Barrel blank (A Tube), while turning it. If the
Spin per Length is not constant but variable, the Twist becomes Progressive.
To look for Information to cut rifle a Barrel, pleas look at Border Barrels. Dr. Geoffrey Kolbe manufactures both button rifled and cut rifled Barrels of high Quality and Reputation, but he speaks more Scottish than English, so I wonder, whether You can understand him.
To cut rifle a Barrel means for repetitively cut small Part from the honed Tube in a Spiral, until all wanted Material is removed. Whether small Machines exist to control the Cutter movement in a progressive Spiral is beyond my Knowledge. Rheinmetall has big Machines to cut rilfe the Panzerhaubitze 200 155 Canon with a progressive Twist up to 9°. The hollow Steel shells are about 6 Calibres long. You see, there was a Predecessor for the LM-105!
Which Law? Where? After the Barrel is finished, no one
can tell, how its made, so the Law cannot be applied to manufacturing
Methods. Easy to distinguish are unrifled Barrels (Shot gun barrels and Sub
caliber Sabot dart barrels ) from rifled Barrels. So Maybe the Lawmaker
meant this Distinction. Please check!
No, I know no Cut rilfler, to make progressive Barrels, but my first stop to ask would be Dr. Geoffrey Kolbe.
LM-105 in flight
I use no 6-DOF Ballistic Programs, as I have no full aerodynamic Data for my Bullets nor any other Bullet. You either need a supersonic Wind tunnel, that I have not, or rather long Calculations with a CFD-Program (that I do have, see above for the LM-105) to get the all - axis - and - spin - data including derivatives to feed into such Program, before it can predict the Path better, than Point-Mass-Programs that I use. For me sound Design after known Principles and Verification later on is the fast, economic and reliable. Therefore i refrain from 6-DOF-Ballistics. Ruprecht Nennstiel comes to Mind, when asking for 6-DOF Experience. Ask him!.
What Application do You look for? Maybe I have something more to offer?
Sincerely, Lutz Möller, email@example.com
Dear Mr. Moeller,
Thank you for your reply, I didn't expect it to be so thorough ☺As for the law, I were just kidding because you know, some target shooters fanatically want their barrels cut, and no other.
I conclude that progressive rifling exist to accommodate (I can't think of a better word) driving bands. Am I correct?
LM: No. Progressive Twist exists to lower the Torque on Bullet and Barrel.
It seems that rifles with PR (which use bullets with driving bands) have more tons of benefit compared to rifles without PR.
So why don't everybody use PR in/on their barrels? I think it's because the supply and manufacturers are still limited. Those condition can exist maybe because the demand is low. The low demand can exist because just a few people know about PR! Do you think it is the case (maybe it's just plain expensive, but a lot of people spend so many $$$ on shooting anyway)?
LM: You can't hammer such Barrel!
And regarding the Haack's paper about minimal drag bullet, do you think "Très Haute Vitesse" was based on this?
LM: The French THV-Pistol-bullet can possibly be designed to be light, hence fast, but still accommodate the original 9x19 Luger length in the Magazine, but that is just my own Assumption, not based on further Knowledge.
Oh, and if I'm not mistaken, it appears that LM-105 ogive is tangential. Usually a bullet with secant ogive have bigger bc than a bullet with tangential ogive (the two bullets have same weight), so why doesn't LM-105 have secant ogive?
LM: No. The
LM-105 uses neither tangent nor secant Ogive, but
Haack's minimal wave drag shape!
Regards, Hans Adhitya
Wait, when I looked at the LM-105 pic you send, I noticed that the drive bands deflects the air that coming towards it, creating a low speed region on the bullet's body (maybe plus some turbulence), which like the tail creates. Does it affects the bullet's accuracy (intuitively I think it's yes, but I don't know by how much)?
LM: With Muzzle brake we (Tom Marstii an Partner ) shot short Range (say 300 m) ½ MoA and won on long Range (say 750 m) on Wind drift. So the Performance was up to the Task.
And why a driving band distance to the previous driving band is decreasing nearing the tail?
LM: Initially you want small Engraving force, but after the
Bullets made some Room, while moving, the Requirement shrank into less stringent
Regards, Hans Adhitya
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