Questions regarding barrel length


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White_Wolf
October 26, 2006, 11:01 PM
Does barrel length affect recoil?

Does barrel length affect the volume of the blast?

From what I hear, a long barrel, up to a point, increases muzzle velocity. To what point does the length of the barrel cease to increase speed? Meaning, what is the longest a barrel can be before its length no longer increases muzzle velocity?

How much difference does barrel length make in muzzle velocity? Example: what is the muzzle velocity difference between a two inch barrel and a six inch barrel?

Does barrel length affect rifling? If so, is there anyway to give me an indication of just how much difference a very short versus very long barrel will make on a bullet’s accuracy and or velocity due to rifling?

The diameter of the barrel determines the maximum diameter of a bullet that can be fired from a gun. But can bullets of infinitely smaller diameter be shot through that barrel. I'll try to clarify the question: You can't shoot a bullet through a barrel that is smaller than the bullet, but can you shoot smaller bullets through the barrel, or are barrels designed to fire one size of bullet only?

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.38 Special
October 26, 2006, 11:11 PM
Does barrel length affect recoil?
In a handgun, yes. I do not know how much it has to do with weight vs. how much it has to with with leverage or other factors that I don't understand, but yes, in general a longer barrel will recoil less than a short one, in a handgun.

Does barrel length affect the volume of the blast?
From a stricly technical standpoint, no, I don't believe so. From a subjective standpoint, yes, it does. In my experience a longer barrel seems to produce less blast than a shorter one.

From what I hear, a long barrel, up to a point, increases muzzle velocity. To what point does the length of the barrel cease to increase speed? Meaning, what is the longest a barrel can be before its length no longer increases muzzle velocity?
Pretty damn long, for most cartridges. I remember reading some piece -- I believe it was Elmer Keith in his autobiography -- that claimed velocity continued to increase until something like 32 feet of barrel, at which point velocity fell off so steeply that bullets began lodging in the barrel.

How much difference does barrel length make in muzzle velocity? Example: what is the muzzle velocity difference between a two inch barrel and a six inch barrel?
There's a great piece in the latest "Handloader" that blows the muzzle velocity myth to pieces. I'd long clung to the idea that MV increased 25 to 50 FPS per inch of barrel, but it just ain't so. Like most of the science of ballistics, you can't count on much of anything when it comes to barrel length. It is safe to say that longer barrel lengths will generally result in higher velocities, but it is not at all safe to assume that two inches of barrel, for instance, will always result in such-and-such amount of velocity increase. In at least one of the Handloader tests, velocity actually increased when an inch of barrel was removed, and then decreased when another inch was removed.

Does barrel length affect rifling? If so, is there anyway to give me an indication of just how much difference a very short versus very long barrel will make on a bullet’s accuracy and or velocity due to rifling?
In terms of mechanical accuracy, any barrel longer than about four inches will give excellent accuracy. Many folks insist that even shorter barrel are capable of excellent mechanical accuracy, though that has not been my experience. In terms of human influence, longer barrels tend to be more accurate, at least with open sights, because sight radius is so crucial to the human eye. Specifically regarding the rifling question, however, I don't actually know what you are asking.

The diameter of the barrel determines the maximum diameter of a bullet that can be fired from a gun. But can bullets of infinitely smaller diameter be shot through that barrel. I'll try to clarify the question: You can't shoot a bullet through a barrel that is smaller than the bullet, but can you shoot smaller bullets through the barrel, or are barrels designed to fire one size of bullet only?
To the best of my knowledge, it is safe to fire undersized bullets in any particular barrel. Accuracy will be non-existant, however, in all but very specialized situations. Bullet diameter must be matched to barrel diameter for any possibilty of accuracy.

White_Wolf
October 26, 2006, 11:47 PM
Specifically regarding the rifling question, however, I don't actually know what you are asking.
Rifling, to the best of my knowledge, refers to grooves set inside the barrel that cause the bullet to spin. The spinning of a bullet stops it from tail-end wobbling and tumbling while in flight. The lack of wobbling and tumbling is what determines accuracy.

Assuming my above understanding about rifling is true, I suppose my question is actually three questions.

1. Will a long barrel give the bullet more of a spin.
2. Is the spin of a bullet what determines its accuracy (as stated above).
3. Assuming the answer to the first two questions is “yes” than to what degree is accuracy affected.

.38 Special
October 27, 2006, 01:45 PM
Rifling, to the best of my knowledge, refers to grooves set inside the barrel that cause the bullet to spin.
Correct.

The spinning of a bullet stops it from tail-end wobbling and tumbling while in flight. The lack of wobbling and tumbling is what determines accuracy.
Close enough for government work.

1. Will a long barrel give the bullet more of a spin.
No. Bullets can be correctly stabilized with less than an inch of rifling. The rate of spin is controlled by the rate of the rifling, measured in turns per inch. One turn in fourteen inches, for example, or one turn in nine inches, usually expressed as "one in fourteen" or "one in nine". Generally speaking, a longer bullet needs to be spun faster than a short bullet for adequate stabilization. There is a formula (the Greenhill formula) for determining velocity/twist/bullet length requirements.

2. Is the spin of a bullet what determines its accuracy (as stated above).
It's an important part of the picture, but a number of other factors have to be in place as well. The bullet needs to be uniform, it needs to enter the rifling undamaged, it needs to exit the rifling in a uniform way from shot to shot (muzzle crown issues), the barrel needs to vibrate uniformly from shot to shot so that it is "pointing" in the same direction each time a bullet exists, and so on and so forth.

3. Assuming the answer to the first two questions is “yes” than to what degree is accuracy affected.
In short, length of rifling isn't a factor in accuracy. The most important "accuracy" function of a long barrel is that it gets the front and rear sights farther apart from one another, thus making small aiming errors more apparent to the shooter.

HTH!

rockstar.esq
October 28, 2006, 12:59 AM
The only part thus far not mentioned is that the bullet appropriate for the bore will actually be cut by the rifling which is what forces the bullet to spin. Although there are some exclusive examples in terms of fragile varmint bullets there's no such thing as "too much spin" for a bullet. Generally speaking the faster twist rates allow more versitility in terms of the projectiles that'll shoot well through it. A common misnomer is that heavier bullets will require faster twist rates. The reason for this is that since all bullets of a given caliber will have the same diameter, heavier bullets are longer than lighter bullets. So more often than not folks refer to bullets by their weight since bullet length is a widely varying feature depending on profile, core composition, and jacket thickness. The "lack of wobbling" thing is actually a way to mitigate slight weight imbalances in the projectile. The tail end of the bullet is actually more influencial to accuracy than the front (properly called the meplat). The deal is that the base needs to be pressed uniformly by the exiting gasses or else one side gets a push that destablilizes the effect of the rifling. In handguns, the double ended wadcutter which is literally a cylinder of lead has long been a match winner in .38 specials. The aerodynamic drag of the flat face has so little effect at handgun ranges that it can almost be ignored!

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