I was watching some show on the Military Channel about tanks and was surprised to learn that a tanks barrel is smooth bore.  Anyone know why this is>

yeah i may have seen the same thing and would also  like to know.

Quoted: I was watching some on the Military Channel about tanks and was surprised to learn that a tanks barrel is smooth bore.  Anyone know why this is>

As I understand it, using rifling wears out the barrel very quickly with current ammunition. That and fin stabilization is much better.

Believe most ammuntion is sabot rounds that are encased in an outer layer that the sabot comes out of when it exits the muzzle then the sabot is stabilized via fins and kenitic energy

Quoted: Quoted: I was watching some on the Military Channel about tanks and was surprised to learn that a tanks barrel is smooth bore.  Anyone know why this is> As I understand it, using rifling wears out the barrel very quickly with current ammunition. That and fin stabilization is much better.

Basically, it turns a rifle barrel into a shotgun barrel - allowing for a much greater variety of ammunition that can be used. eg: APFSDS, rockets, flechette. (the Russians for one use Rockets, Israelis use flechette and buckshot in their tanks. Not sure what interesting ammo the American tankers get to use)

our tank is a smooth bore, it fire high vel sabots(along as he and such) that are big metal(DU) darts that blow a hole thru a tank, the force will suck a goat out the little exit hole(they did tests), and not only will it blow the hell out of the tank its made from du that when fragments/ powders it combusts. The challenger has a rifled bore, they use HEAP rds, our rounds penetrate more armor but the brits tank has the longest shot kill record to date.

As I understand it, the length of the projectiles for the given mass would require a very high rate of twist to properly stabilize gyroscopically.  (Think 120 grain projectiles from a .223.  1-in-7" wouldn't cut it.)

The projectiles used in tank cannon, then, are aerodynamically stabilized, like darts.  With the fire-control computers onboard, they can be pinpoint accurate.  But we don't use aerodynamically stabilized bullets in small-arms because of the size of the projectile makes this unsuitable from a physics perspective.  Plus, a smoothbore cannon can fire at much higher velocities, and in a direct-fire weapon, speed is life.

However, large-bore indirect-fire artillery is still rifled.  The projectiles used there are much shorter, and more "bullet-like."  Gyroscopic stabilization works fine.  Mortars, however, used aerodynamically stabilized projectiles (very short barrels, need all the velocity they can get, I assume.)

????? looks like rifling to me...

Quoted: ????? looks like rifling to me... img377.imageshack.us/img377/535/challenger25pb.jpg

Its a Brit tank, the brits use a rifled gun.  

that is because that is a pic of a challenger, which as the poster above pointed out, has a rifled bore.

ETA: Beat me to it.

ah

So why are tank barrels smooth bore?

Discarding Sabot Fin Stabilized Anti Tank rounds are more efficient in a smooth bore.

We placed priority on anti tank capability due to the cold war USSR tank threat.

Rifled bores are better for just about everything else.

Smooth bore allows the higher velocity needed for the AP rounds developed to fight Soviet armor on the Eastern European steppe.


ETA: Dangit, beat me to it while I type with all ten thumbs.

The British are the exception to rule. They have maintained the use of a 120mm rifle ever since the Conqueror days of the mid 1950s. (They've been improving the gun, of course, to maintain current standards). Most guns on tanks these days (Russian, German, French, Japanese, Israeli) are smoothbored.

The reason being that they can fire a more effective variety of ammunition than a smoothbore can. (I realise that this seemingly contradicts an above poster)

Advantages to smoothbore:
Decreased barrel wear.
Increased pressure because the gasses can't escape down the rifling: Higher velocity.
Cheaper ammunition.
HEAT rounds are more effective when not spun.

Advantages to rifling:
More accurate at longer range (Current kill distance record is held by a rifle, 5,300m)
Projectiles do not need to devote any of their volume to accounting for stabilisation fins, hence a higher payload.

Basically, a smoothbore is a better tank-killing weapon, though the L30 firing the current generation fin rounds on Challenger 2 is certainly no slouch.

A rifle is a better general purpose weapon. Currently, for example, the only HE round available for the German smoothbore is one that the Swedish came up with by converting a mortar bomb. And no, the Americans haven't bought it. The spin problem with HEAT is completely sidestepped by the British because their default round is HESH. (American equivalent HEP). The larger rifle-fired projectile carries more explosives making it far more effective against troops and structures.

I cannot think of any round that the smoothbore can fire that cannot be effectively fired from a rifle. However, when the tank started to lose its infantry support role and turn into a tank killer, the cost/benefit ratio of a smoothbore became much more attractive, and if I don't miss my guess, the Russian T-62 was the first to be mass-produced with one. (115mm).

Yep for APDSFS rounds.  The silver bullets are  fin stablized, spin imparted by a rifled barrel decreases its stability in flight.  They used to use some kind of ball bearing (or something like that) outer ring to reduce the spin produced by the rifled barrel, eventually just went smooth bore because that didn't work so well.


ETA forgot about the HEAT round being better of not spun as mentioned above

From what I hear, we could use a good general purpose HE round.....right now or sooner.  

Curiously, the Army has actually figured that out. There is currently a move to try to replace HEAT, MPAT, HE-OR and Cannister rounds with a single multi-function explosive round.

I don't think it'll work. Each has their own states of advantage. Replace HEAT with conventional HE, maybe you can ditch the HE-OR round and replace with the HE round as well if you build it right. Otherwise, keep MPAT and cannister for those situations where a HE round really isn't the best thing you could shoot.

The most recent thread on Tank-net on the subject has a reasonably detailed post on why the British stayed with the rifle. (Basically what I wrote above!)

63.99.108.76/forums/index.php?showtopic=11080&hl=mpat&st=0

Edited: Here's an even better (4 page) thread on the subject.
63.99.108.76/forums/index.php?showtopic=8014&hl=

NTM

Quoted: Curiously, the Army has actually figured that out. There is currently a move to try to replace HEAT, MPAT, HE-OR and Cannister rounds with a single multi-function explosive round. I don't think it'll work. Each has their own states of advantage. Replace HEAT with conventional HE, maybe you can ditch the HE-OR round and replace with the HE round as well if you build it right. Otherwise, keep MPAT and cannister for those situations where a HE round really isn't the best thing you could shoot. NTM

I read an article about that, its going to take a few years and its not a sure thing, funding wise.

I wish they would just buy something from the Israelis or someone, and get it out to you guys NOW.

Manic_Moran

Finally found the time to look at your Iraq photo pages, great stuff.

Thanks for sharing them!

"Danger Bunnys"

It's easier to clean. We wouldn't want to confuse our tankers, after all. j/k

The French AMX-30 from the 70s on used a rifled gun, but their primary anti tank round was a shaped charge round which performed best when the blast jet did not spin.  So they apparently had ball bearings within the shell to hold the charge portion relative stationary.  Which always sounded bizarre.  

But it is an example of why a tank might want a smoothbore.  

sabots

longer lasting

old school musket like

Was the German 88 rifled?

Anybody know offhand?

Quoted: Was the German 88 rifled? Anybody know offhand?

I know this show said the Sherman gun was rifled.  Thats not what you asked but I found that interesting.

Quoted: Was the German 88 rifled? Anybody know offhand?

Yes.

Quoted: Quoted: Was the German 88 rifled? Anybody know offhand? Yes.

That was a badass field rifle! Didn't the use them on both field rifles AND tanks?

The REAL answer?  Because the long rod penetrator would need an impossible rifling rate to stabilize.

The rate of twist is determined by the length to diameter ratio.  It matters not one bit on weight, except for the mass distribution.  But small diameter, long projectiles need faster spins.

Just imagine a 50 pound flywheel spinning like a top.  Pretty easy to do if it is 4 feet in diameter but try spinning a 50 pound rod, 1 inch in diameter.

Since a rod penetrator cannot be spun, any rifling is ineffective.  

This is approximated in small arms using the Greenhill Formula.  Twist for stable flight is equal 150 times the diameter of the bullet in inches squared and divided the length of the bullet.  Using a 12" long, 1" diameter penetrator (not actual), the twist rate is one turn in 12.5 inches.  For a 120 mm bore (4.724"), this is like a one turn in 2.646 inches in our little ..2245" bore AR 15.  That is an impossible twist rate.

Quoted: Quoted: Quoted: Was the German 88 rifled? Anybody know offhand? Yes. That was a badass field rifle! Didn't the use them on both field rifles AND tanks?

It was used for anti aircraft, anti tank (towed), anti everything, and tank mounted of course.

Quoted: Quoted: Quoted: Quoted: Was the German 88 rifled? Anybody know offhand? Yes. That was a badass field rifle! Didn't the use them on both field rifles AND tanks? It was used for anti aircraft, anti tank (towed), anti everything, and tank mounted of course.

I thought it was used to "Kill then enemy".
Be it planes, trains, tanks, subs, men or cars. If it walked, trotted or putted or zoomed, the 88 would kill it.

Quoted: Quoted: Quoted: Quoted: Quoted: Was the German 88 rifled? Anybody know offhand? Yes. That was a badass field rifle! Didn't the use them on both field rifles AND tanks? It was used for anti aircraft, anti tank (towed), anti everything, and tank mounted of course. I thought it was used to "Kill then enemy". Be it planes, trains, tanks, subs, men or cars. If it walked, trotted or putted or zoomed, the 88 would kill it.

I think I covered that with "anti everything."    

Quoted: The REAL answer?  Because the long rod penetrator would need an impossible rifling rate to stabilize. The rate of twist is determined by the length to diameter ratio.  It matters not one bit on weight, except for the mass distribution.  But small diameter, long projectiles need faster spins. Just imagine a 50 pound flywheel spinning like a top.  Pretty easy to do if it is 4 feet in diameter but try spinning a 50 pound rod, 1 inch in diameter. Since a rod penetrator cannot be spun, any rifling is ineffective.   This is approximated in small arms using the Greenhill Formula.  Twist for stable flight is equal 150 times the diameter of the bullet in inches squared and divided the length of the bullet.  Using a 12" long, 1" diameter penetrator (not actual), the twist rate is one turn in 12.5 inches.  For a 120 mm bore (4.724"), this is like a one turn in 2.646 inches in our little ..2245" bore AR 15.  That is an impossible twist rate.

Whilst true, the sabot rounds fired by rifled tank cannons have been fin stabilised for decades, so that argument is a bit of a non-starter. Does complicate things though.

NTM

Quoted: Quoted: The REAL answer?  Because the long rod penetrator would need an impossible rifling rate to stabilize. The rate of twist is determined by the length to diameter ratio.  It matters not one bit on weight, except for the mass distribution.  But small diameter, long projectiles need faster spins. Just imagine a 50 pound flywheel spinning like a top.  Pretty easy to do if it is 4 feet in diameter but try spinning a 50 pound rod, 1 inch in diameter. Since a rod penetrator cannot be spun, any rifling is ineffective.   This is approximated in small arms using the Greenhill Formula.  Twist for stable flight is equal 150 times the diameter of the bullet in inches squared and divided the length of the bullet.  Using a 12" long, 1" diameter penetrator (not actual), the twist rate is one turn in 12.5 inches.  For a 120 mm bore (4.724"), this is like a one turn in 2.646 inches in our little ..2245" bore AR 15.  That is an impossible twist rate. Whilst true, the sabot rounds fired by rifled tank cannons have been fin stabilised for decades, so that argument is a bit of a non-starter. Does complicate things though. NTM

That is because a saboted round, having smaller diameter, cannot be stabilized as easily in the larger bore's twist rate.  

The real answer?

It is because western tanks were optimized towards killing other tanks at the Fulda Gap in Germany.  Kinda like the groundpounders version of the "not one pound for air to ground" philosophy in developing the F-15.  

Bradleys can fight infantry, and be able to defend themselves against other APC's.  

That long DU penetrating rod is best fired from a smooth bore, so a smoothbore cannon it shall be.

Heh.  Now that is a twist.  In WW2 US tanks were originally geared towards fighting infantry, and tank destroyers were optimized towards intercepting tanks.

Which brings us right back to the question of 'what is a tank's job'?

This question makes a mockery of the traditional 'what is the best tank' question, since almost invariably the argument comes down to "But the SuperPanzer VII will beat the Megatank IV three times out of four' or whatever, whilst completely forgetting that the true role of a tank is to help the infantry. (Cavalry operations in the enemy rear are another possibility, but these days usually with Mech inf in accompaniment)

Most smoothbore tanks are optimised to become tank destroyers with a seconday tank role. The rifled tanks that are left are primarily tanks which accept the minor penalties in the tank destroying role in order to be very good at their originally envisioned purpose.

NTM