How exactly do longer gun barrels increase bullet velocity?

Question

From what I understand, longer gun barrels increase a bullet's velocity. But I don't understand the reasons why that is true. It would seem to me that the longer a gun's barrel is, the more friction and resistance the bullet would encounter as it moves along the rifling. So how is it that velocity increases with gun barrel lengths, and, also, does velocity continue to increase the longer and longer a barrel becomes? If I had a gun barrel a mile long would the bullet come out at unbelievable velocities?!

***I asked this question in Hunting category and got no response, so I will try it here....***

Answer 1

isn't it because of the trapped gas that "pushes" the bullet, so the longer the pressure is held(longer barrel), the more force it exerts? Just a thought.

Answer 2

As far as I know the barrel has nothing to do with bullet velocity.  However guns with higher velocity rounds (velocity is determined by the bullet not the gun) tend to have longer barrels for increased accuracy.  

Answer 3

Remember the difference between speed and velocity: velocity is speed given a direction. A longer gun barrel would maintain a constant direction for a longer period of time. Therefore, the velocity is increased as well. A shorter barrel would mean that the bullet would be in the air longer, which is taken for granted by other factors (air friction, wind, gravity, etc.).

Answer 4

The gun powder does not detonate all at once like, say, a stick of dynamite. If it did, the barrel would explode from the shock wave. Instead, it releases combustion gases more slowly (less than a millisecond instead of microseconds). This creates a rapidly increasing gas pressure from combustion products behind the bullet. It's this pressure acting over the entire time the bullet is in the barrel that accelerates the bullet to high speed. After the powder finishes burning, the pressure starts to drop again as the gas volume expands behind the traveling bullet (still in the barrel), but it's still quite high up until the time the bullet exits. Any pressurized gas left in the barrel after that expands in all direction and no longer contributes. It's this released gas that makes the characteristic "bang". So, the longer the barrel, the longer that gases can perform work on the bullet and the faster it goes. Pistols are generally louder than rifles of the same caliber because the released gas has a higher pressure (not having had a chance to expand as much).

Answer 5

Conservation of Angular Momentum helps with accuracy.

Due to the rifling (which imparts spin to the bullet as it travels along the bore), the projectile has a vector of angular momentum along the axis of the bore and will tend to maintain it's orientation so the tip is always forward in flight.

I'm not sure that the velocity is increased with longer gun barrels, but the angular momentum sure could be.

Answer 6

it gives the projectile a longer time to build up speed less wind resistance regardless of how short the time(every bit counts) and also it has more riflings (longer grooves) in the barrel, enabling the projectile to spin faster which also increases velocity. the friction and resistance is only a small factor to wind resistance as all the while, inside the barrel, the projectile is being propelled by gases caused by the explosion of cordite that is still trapped within the breach of the weapon ( not the gun). friction tends to heat the projectile almost to a point of disfigurement (is that a word?) that's why if you have ever been hit by a round, at first you don't feel it then all of a sudden this burning sensation sets in until the heat is un bearable ouch! I imagine that if a barrel from a rifle was a mile long the projectile would melt down within. keep in mind the engineers who design these weapons are very smart and do extensive live fire testing until what they developed a product that is up to standard.

Answer 7

Forgetting all of the bits about speed V velocity, and cutting things right back to the basics.

There is a maximum amount of power in cartridge. This determines how far and how fast the bullet can go. Nothing will make it go any more than this maximum.

If you have a short barrel some of this power escapes early. The longer the barrel the less power escapes early and the more it can be used to push the bullet, however when you get to a certain length of barrel you've reached the maximum so any more length won't make a difference.

Answer 8

the longer the barrel is the more chance the pressure has to build up which actually increases its velocity squared by the cubic centimeter's