Posted on 05/14/2010 8:23:57 PM PDT by OneWingedShark
I was wondering about gun-smithing recently. Particularly rifling; I don’t know anything about the actualities of smithing, so it’s pure conjecture on my point.
Given a rifled barrel, they have constant rifling rates, is it possible to make ‘varying rate’ barrels.
Would such a varying rate reduce the wear on barrels?
To help clarify what I'm trying to get at, here are some pictures.
A constant rifling of 2 rotations per unit-length.
A variable rifling [ignore the negative portions] which starts at '0' {the rifling being parallel to the major axis of the barrel} to '8' which is the desired rate of spin to impart to the bullet. (with constant rate-of-change)
A variable rifling which changes at a varying rate-of-change, instead of a constant.
The RPM will increase, twist per inch won’t, unless the barrel has gain twist. Imparting spin to a projectile increases pressures so a gain twist may help even pressures out with fast burning smokeless powder.
Old habits die hard.
A well made black powder rifle is a precision tool, not at all like a musket.
Optimum twist is linked to bullet length and diameter, minor pitch rate variations may have a drastic effect on accuracy. There would be no point in decreasing pitch just before the bullet exits, trying to do so would only introduce more forces likely to deform the bullet and cause the core to loosen in the jacket. A loose core will cause all kinds of instability.
Interesting; thank you for the info.
Since we’re on the subject of Rifling, does anybody have any insight on how exactly are barrels rifled – ie. What type of machine process is used to rifle a barrel?
Broaching?
Milling?
As I understand it, when the bullet makes the jump from the cylinder (not rifled) to the barrels forcing cone where the rifling begins, the high speed and heavy weight of the .460 bullet would cause considerable torque if it was run up to it's terminal rotational speed immediately.
Gain twist rifling IIRC is also used on 16" naval guns.
There are several methods; check out:
http://en.wikipedia.org/wiki/Rifling
under the ‘Manufacture’ section.
Not entirely. In light automatic artillery, it's been used to prevent the failure of nosefuze arming safeties to prevent premature detonation of explosive projectiles while still inside the barrel due to excessive initial centrifugal shock.
Likewise, in small arms progressive rifling can be helpful in both smaller calibers to prevent shredding the metal jackets of rifle-caliber bullets driven at high velocity, and in handguns, to prevent leading of barrels with large diameter soft projectiles as they make the transition from a revolver's forcing cone into the barrel's rifling. The latter is likely the reason that S&W adopted gain twist rifling for their .500 S&W fiveguns.
Broaching?
Milling?
Broaching is suitable for some initial operations in barrel productions, the *raw stock* naterial being referred to as a *blank.*
However, the Appel cold forging rotary process, also known as *hammer forging* or rotary forging, of the finished tube over a mandrel via cam-driven machine impact devices produces barrels that are as consistant as the mandrel upon which they are formed, and is used for everything from smoothbore artillery barrels to rifle and MG barrels to hypodermic needles.
Info and background here and here
More on hammer-forged barrels as applied to small arms here and here [.PDF]
Actually, no.
When the bullet changes speed, the RPM changes. The rate of twist, for example one turn in nine inches, remains constant in standard rifling.
As noted, it’s been done, but it is extra work for a questionable benefit. First, it actually distorts the bullet more than constant twist rifling becuase the grooves in the bullet have to expand to accomodate the grooves in the barrel when the twist turns to a sharper curve.
Second, it takes more work. It’s not so bad now with CNC machines, but before then, the machinist needed a lathe that could change speeds very precisely, and repeat the function exactly each time the tool passed through the barrel.
I think everyone knew what I meant.
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