Rifled barrel question [Archive] - Glock Talk

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RWBlue
03-20-2012, 11:05
In the beginning, we had smooth bored guns. They were not accurate at longer distances.

Then we had someone make rifled barrels. They were more accurate at longer distances.

Now we have Abrams tanks with smooth bored cannons, that are accurate...WTF?

105 mm L52 M68 rifled cannon (M1)
120 mm L44 M256 smoothbore cannon (M1A1, M1A2, M1A2SEP) with 42 rounds

I don't get it. How is a smooth bore an improvement over a rifled bore?

arclight610
03-20-2012, 11:07
The rounds are fin-stabilized

TN.Frank
03-20-2012, 11:23
The rounds are fin-stabilized

Along with Laser guided and GPS too.
The whole rifling deal started because some gunsmith somewhere wanted to cut grooves into the barrel to collect fouling from the black powder so they could load more before they needed to clean. First they were just straight grooves in the barrel. Then someone got the bright idea of making the grooves spiral so they'd be longer and hold more fouling and pretty much by accident they found that this style of barrel was also more accurate. I guess it didn't take them long to figure out it was because the bullet was being spun in flight. Some said that with the round ball spinning it allowed a demon to stay on the bullet better to help guide it, they sited that the Earth spun round and it was full of demons.
The real facts are that with the ball spinning any heavy spots get moved around during flight so it'll not be pulled to the heavy side of the ball and just like a gyroscope it wants to remain stable during flight and not be moved off course.
Funny how things come about like that.

m2hmghb
03-20-2012, 11:58
Along with Laser guided and GPS too.
The whole rifling deal started because some gunsmith somewhere wanted to cut grooves into the barrel to collect fouling from the black powder so they could load more before they needed to clean. First they were just straight grooves in the barrel. Then someone got the bright idea of making the grooves spiral so they'd be longer and hold more fouling and pretty much by accident they found that this style of barrel was also more accurate. I guess it didn't take them long to figure out it was because the bullet was being spun in flight. Some said that with the round ball spinning it allowed a demon to stay on the bullet better to help guide it, they sited that the Earth spun round and it was full of demons.
The real facts are that with the ball spinning any heavy spots get moved around during flight so it'll not be pulled to the heavy side of the ball and just like a gyroscope it wants to remain stable during flight and not be moved off course.
Funny how things come about like that.

The 120mm shells are not laser guided. There is a ballistics computer inside the tank that checks the barrel for warpage, adjusts for rounds fired, takes into account the humidity and temperature to get an accurate trajectory for the shell to fly on.

1gewehr
03-20-2012, 14:13
No comparison between the old muskets and the 120mm gun.

The tube on a 120mm is one of the most accurately-machined pieces of steel on the planet. The bore is as absolutely straight as science can make it. The reason it is a smoothbore is so that they could get every possible last bit of velocity out of it. It is the velocity that enables the solid projectile to go through another tank's armor.

The projectile as mentioned above is fin-stabilized, like an arrow. The design is supposed to give all the stabilization needed with the least amount of drag.

Watching those things fire at night is amazing! The muzzle flash lights up the night, and the projectile goes so fast and straight that the tracer looks like a laser-beam!

WoodenPlank
03-20-2012, 14:50
The rounds are fin-stabilized

Bingo. The APFSDS rounds look like lawn darts from hell.

http://upload.wikimedia.org/wikipedia/commons/2/26/Sabot_separating.gif

Here's a couple of Wiki (http://en.wikipedia.org/wiki/Kinetic_energy_penetrator) articles for your reading (http://en.wikipedia.org/wiki/M829) pleasure...

Brian Lee
03-20-2012, 14:56
..............The real facts are that with the ball spinning any heavy spots get moved around during flight so it'll not be pulled to the heavy side of the ball and just like a gyroscope it wants to remain stable during flight and not be moved off course.
Funny how things come about like that.

This does not account for the fact that even with a perfectly balance ball the lack of accuracy still persists.

I think it's really because with no spin, there can be random end-over-end tumbling in flight, causing the ball to generate aerodynamic forces that make it curve just like a golf ball, or a curve ball thrown by a baseball player. Since the tumbling of a round bullet that was launched with a cloth patch can be in almost any direction, and at almost any rotational speed, you can never predict which way the curve ball will curve. An axial spin prevents this tumbling, so the curve ball effect goes away.

Decguns
03-20-2012, 21:31
The Abram's fire control computer is much like an aircraft's ballistic computer. Takes into account everything from barrel droop, ambient heat, elevation, ammo temperature, humidity, barometric pressure, curvature of the earth, how far the earth will move during projectile flight, vehicle speed, etc...

Haldor
03-20-2012, 21:42
This paragraph from the wiki article linked to in post 6 explains this very well.

http://en.wikipedia.org/wiki/Kinetic_energy_penetrator

The APDS was initially the main design of KE penetrator. The logical progression was to make the shot longer and thinner to concentrate the kinetic energy in a smaller area. However a long, thin rod is aerodynamically unstable; it tends to tumble in flight and is less accurate. Traditionally, shells were given stability in flight from the rifling of the gun barrel, which imparts a spin to the round. Up to a certain limit this is effective, but once the projectile's length is more than six or seven times its diameter, rifling becomes less effective.

Adding fins like the fletching of an arrow to the base gives the round stability, hence Armour-Piercing Fin-Stabilized Discarding Sabot (APFSDS). The spin from rifling decreases the effective penetration of these rounds (rifling diverts some of the linear kinetic energy to rotational kinetic energy, thus decreasing the round's velocity and impact energy) and so they are generally fired from smoothbore guns;