Why smoothbore main gun?

[M1A1HA]

Almost all modern MBT use smoothbore main gun. If I am not mistaken, many WW2 tanks use threaded gun with muzzel break. Why? Thanks.

[Mark IV]

Smoothbore means higher muzzle velocity- no rifling in the barrel to increase friction.

The rounds are stabilized by fins, instead of spinning.

[Jon_S]

Post-war searching of the Nazi archives discovered proof that Hollow Charge rounds became dizzy and dis-oriented if spun too fast. The Germans were working on a solution to this problem, but luckily had only come up with the Panzerfaust and the Panzerschreck before the war ended.

After the war the americans used press-ganged german scientists to work on this problem. After a few false starts involving Kitchen Sinks and the Mars Polar Lander, they eventually developed the 120mm smoothbore.

Interestingly, the UK was only able to grab some low grade Nazi scientists. These 2nd-rate boffins were only able to come up with the Mini and the Millenium Dome. This is why the Challenger II still uses a rifled 120mm main gun.

Regards

Jon

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Ubique

[This message has been edited by Jon_S (edited 06-15-2000).]

[Lorak]

thanks Jons, that explains it.

Lorak

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http://clubs.yahoo.com/clubs/combatmissionclub

Lorak's FTX for CM <--Proud member of the Combat Mission Webring

[Kevin Peltz]

M1:

It was found that the spinning of HEAT rounds caused the plasma-jet effect to dissipate instead of focusing on a tiny spot on the armour plate, causing loss of penetration. It is also easier to manufacture APFSDS (Armour Piercing Fin Stabilized Discarding Sabot) ammo if rifling does not need to be taken into account. With the sabot, there is more than enough room for the addition of fins to be added to the penetrator. (I believe that the 120mm gun on the Abrams fires a 40mm penetrator, once the sabot has flown clear...

[Mad_Merse]

MarkIV is right about the lack of rifling reducing friction for kinetic kill rounds (APDS, APFSDS, etc). That, in turn, should lead to extended cannon tube life and reduced wear. The reduced wear has two benefits 1) Extended tube life and 2) Retention of tube accuracy. With today's very fast, heavy projectiles, tube erosion is a real issue.

High Explosive Anti-Tank (shaped charge rounds relying on the Munroe effect for penetration) will have their penetrating capabilities very adveresly affected by spinning. The spinning prevents the proper formation of the metal particle jet which causes the penetration of the tank's armor. If the tube is rifled then a rotator band that both seals the barrel with the propellant gases behind it and allows the HEAT round to travel the length of the barrel without imparting spin from the rifling.

So given the benefits for the kinetic rounds, and a simpler HEAT round design, most nations have gone to smooth bore cannon for their Main Battle Tanks (And if you're a CIS design, you can also shoot ATGM from a smoothbore).

Bob Mercer, Geekoid

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"Next slide, next slide, you swine! Do you want to brief forever?" Apologies to Frederick the Great

[Dittohead]

So what happens when you fire Black Sabot through a smoothbore gun?

Tony

[M1A1HA]

Sorry for my ignorance. "stabilized by fins" Is that means fins will stick out after fired? Thanks Mark and Jon.

[Guest Germanboy]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Jon_S:

After the war the americans used press-ganged german scientists to work on this problem. After a few false starts involving Kitchen Sinks and the Mars Polar Lander, they eventually developed the 120mm smoothbore.

<HR></BLOCKQUOTE>

Err, excuse me but isn't the 120mm in the M1 the Rheinmetall gun used in the Leopard II? Which is produced under licence in the US?

But do go on about the Americans' attempts at reproducing the Schwere Volksspüle.

Andreas - patriotic for a change.

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Andreas

The powers of accurate perception are often called cynicism by those who do not possess them. (forgot who said it)

[Mark IV]

Yes, the Russian ones at least have spring-loaded fins like a 1950s rocket ship that pop out when the sabot is discarded. They keep the round straight, like the fletching on an arrow.

[Jon_S]

Um, my 1st post was mostly a joke. Note to self: self, work on humour.

Bits of it were serious though. Instead of just giving you badly remembered "sound-bites" of info, check out the following sites for info on the M1, and its ammo:

http://www.fas.org/man/dod-101/sys/land/120.htm

http://www.fas.org/man/dod-101/sys/land/du.htm

http://www.fas.org/man/dod-101/sys/land/m1.htm

Regards

Jon

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Ubique

[This message has been edited by Jon_S (edited 06-16-2000).]

[Guest Germanboy]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Jon_S:

Interestingly, the UK was only able to grab some low grade Nazi scientists. These 2nd-rate boffins were only able to come up with the Mini and the Millenium Dome. This is why the Challenger II still uses a rifled 120mm main gun.

<HR></BLOCKQUOTE>

It is also the reason why UK kitchen sinks are still equipped with two tabs, one for hot, one for cold water.

Note to self, must read posts closer and not post after three glasses of Raki.

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Andreas

The powers of accurate perception are often called cynicism by those who do not possess them. (forgot who said it)

[Wayne]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Mark IV:

Smoothbore means higher muzzle velocity- no rifling in the barrel to increase friction.

The rounds are stabilized by fins, instead of spinning.<HR></BLOCKQUOTE>

Sound like the main gun on a tank is a rocket launcher.

[Berlichtingen]

<BLOCKQUOTE>quote:</font><HR>After the war the americans used press-ganged german scientists to work on this problem. After a few false starts involving Kitchen Sinks and the Mars Polar Lander, they eventually developed the 120mm smoothbore.<HR></BLOCKQUOTE>

The US has yet to develope a 120mm... the one we use was developed by the Germans for their Leopard II. Come to think of it, the US has yet to develope a high volocity gun of any size.

[Mark IV]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Wayne:

Sound like the main gun on a tank is a rocket launcher.<HR></BLOCKQUOTE>

M60A2 was. 152mm main gun that fired the Shilleleagh missile (sp?- yukkie thing to shoot at the Red Army).

But a rocket contains its own propellant (keeps burning after it leaves the tube), while most tank guns fire just like a rifle- they set off an explosion in a tube and let that pop Mr. Bullet out. From there on, it's all kinetic energy... momentum. The only difference between rifled and finned AP ammunition is how you stabilize the projectile in flight.

In the "gun" idea, rifling in the bore of the gun caused the big bullet to spin, which stabilizes very well. Fins do the same thing without eating up energy down the bore of the gun (but they are a later technology).

Rockets keep going by burning propellant in mid-flight, but at relatively low velocities (they usually use some kind of shaped charge as a warhead, which blows a hole in armor from outside) that does not depend much on the velocity of the projectile for killing an armored target.

Armored piercing ammo tries to send the whole solid bullet through the enemy tank by launching heavy, dense things going faster than hell. Smooth-bore, fin-stabilized armor-piercing rounds go even faster than "faster than hell". AP rounds are generally more effective on thick frontal armor and are harder to defeat with counter-measures, like reactive armor (which explodes in self-defense to defeat shaped-charge things).

Solid armor piercing ammo is still the "primary armor-defeating round" as far as I know.

[Maastrictian]

Kevin Peltz wrote:

<BLOCKQUOTE>quote:</font><HR>

It is also easier to manufacture APFSDS (Armour Piercing Fin Stabilized Discarding Sabot) ammo if rifling does not need to be taken into account.

<HR></BLOCKQUOTE>

This statement is a tautaulogy (well... maybe not technically). The original sabot round was APDS, it was not fin stabalized because there was no need, the round spun. Making APFSDS is *only nessisary* if you have a smooth bore barrel.

M1A1HA wrote:

<BLOCKQUOTE>quote:</font><HR>

Sorry for my ignorance. "stabilized by fins" Is that means fins will stick out after fired? Thanks Mark and Jon.

<HR></BLOCKQUOTE>

If you mean: "stabilized by fins that pop out like on a ATGM" you are incorrect. The fins of the APFSDS round are fixed.

Mad_Merse wrote:

<BLOCKQUOTE>quote:</font><HR>

High Explosive Anti-Tank (shaped charge rounds relying on the Munroe effect for penetration) will have their penetrating capabilities very adveresly affected by spinning. The spinning prevents the proper formation of the metal particle jet which causes the penetration of the tank's armor. If the tube is rifled then a rotator band that both seals the barrel with the propellant gases behind it and allows the HEAT round to travel the length of the barrel without imparting spin from the rifling.

<HR></BLOCKQUOTE>

Not only is the round simpler, the explosive part is wider. The rotator band takes up width and it turns out that HEAT penetration is directally proportional to the size of the explosive's width.

As a final historical note, the smooth bore cannon was really developed in the 70s, when HEAT was king of the battlefield (before composite and reactive armor). Because a HEAT round can penetrate something like 600mm of flat steel, there was simply no way to armor a tank suficiently. And little reason to fire anything else (well, sabot does have a flatter trajectory for long range shots). The German Leapord II tank was designed in responce to this (as one example) and it focused on manuverability. It has *very* light armor (not enough to stop a hit by sabot or HEAT at any range) and doctrine says that is should just move as fast as possible and as erratically as possible to make it hard to hit.

The smooth bore cannons of the 70s and early 80s are designed to fire HEAT (the ultimate round of the period) not sabot (argueably the ultimate round of this). So the FS of APFSDS is a *consession* to smoothbore. APFSDS is actually less acurate than spin stabalized APDS.

But heck, that's all IIRC. I'm pretty sure I'm right though

--Chris

p.s. Holy....... um.... moly! I'm a member... only took me two months... (I obviously only post when I have something particularly irritating to say.)

[This message has been edited by Maastrictian (edited 06-16-2000).]

[Supertanker]

Here, this link has a picture of various 120mm ammunition, and also a picture of the sabot falling away from a penetrator. You can see the fins on the back of the penetrator if you look carefully:

http://www.atk.com/conmun/descriptions/120mm-tank-ammo.htm

The cylindrical rounds with the stick on top are HEAT, the APDS ammo are the pointy ones. Dunno what the others are.

[Kevin Peltz]

That's spelled tautology- if you want to nitpick, at least try to spell it right. Or, should I say that another way?

[Murx]

Hehe, on the link the part (quote)

Interoperable with the Leopard 2 NATO 120mm smoothbore tank cannon

sounds like the 120mmm smoothbore is a US-product, in fact it isn't (trying rest on the Germans laurels ?).

The APFSDS (in German KE - kinetic energy) round has a 120mm diameter and the projectile itself is 40mm in diameter, weighting something like 3Kg (6 pounds for you non-metrics

The problem with these guns (and it's main advantage) is to get it chromed inside evenly. As it's more then 1.5 squaremeter to cover with less then 15 square centimeter not covered it's very hard to produce.

But the advantage is that even after 1000! (one-thousand!) rounds there was no notably use on the barrel! So it's practical undestroyable through use! It's even selfcleaning, meaning if you shoot the round will clean the inside.

The training ammo is (as we said made of beton) formed in a way that it's instable after 4 Km and will only fly max 12 Kms, the war-rounds (APFSDS) could fly nearly up to 100Km (but that wouldn't be aimed and the projectile will just make a clonk on the ground..)

The cartridge(? right word ?) is made of a solid bottom with a electric fuse and a ignition needle that expands through the complete powder section, But the powder itself is hold together bymillboard ( ? Pappe ?). So there is not much left for the loader to get rid off

murx

[This message has been edited by Murx (edited 06-17-2000).]

[Mark IV]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Maastrictian:

As a final historical note, the smooth bore cannon was really developed in the 70s, when HEAT was king of the battlefield (before composite and reactive armor...The smooth bore cannons of the 70s and early 80s are designed to fire HEAT (the ultimate round of the period) not sabot (argueably the ultimate round of this)<HR></BLOCKQUOTE>

Our M60 series main battle tanks were armed with the British-designed M68 105mm. At the Armor School in Fort Knox, in 1977, we were taught that the APDS was our "primary armor defeating round" and that HEAT rounds were for flank/rear shots on Soviet tanks and softer IFVs (in other words- don't waste your sabots on BMPs and BRDMs). This philosophy was matched by the standard load-out, which was mostly sabot.

Murx: Metric conversion is a little off, there. 3kg is more like 6 1/2 pounds.

[This message has been edited by Mark IV (edited 06-16-2000).]

[Trooper]

There's a bit of a discussion on this over on tanknet.org (Look under the 'Scientific' section for 'fin-stabilised out of a rifle').

I personally do not berate the UK for either having two faucets on their sinks (Makes fixing them so much easier) or having rifles for their main guns. Personally, I think they probably have it right. by eliminating the need to have room for fins in the design of the projectile, they can have lots more explosive in the HESH (and do they also have HE?) rounds, resulting in a much more satisfying bang. Challenger is probably the most capable NATO tank against infantry, structures and fortifications, at the cost of a slight reduction in its anti-armor abilities. Jack of all trades, master of none, I guess, but I support them.

[Trooper]

Oh, by the way, Berlichten.. The US has developed 120mm guns in the past. The T43 (Later the M103) entered full scale service in 1957 armed with the M58 120mm cannon, which used separate ammunition. Then in the Early 1970s, Chrysler's K-Tank design had a 120mm gun as well. (Named Delta apparently).

Of course, I'm not begrudging the US's ability to borrow and then redesignate... (British armor, Italian sidearms, Swiss LAVs, Swedish LAWs....)

[:USERNAME:]

Just from an engineering standpoint i can say that discarding sabot ammo from a rifled barrel would be less accurate than from a smoothbore. The rifled ammo would have to be extremely balanced with precision centering of the penetrator and matched wieghts of the sabot shoes (expensive). There could be no provision for fins because of the spin. I believe almost all sabot and hVAP ammo in WWII was inaccurate.

HEAT rounds are of course unstable when spun (as well as reducing the penetration effects) because any object with a hollow in the front will tend to wobble and "go stupid". This usually limited range to below 500 meters in WWII for HC. The Germans in WWII were probably the best at HC Xray photos and were aware that the liner remined really a "solid" even back then.

WWII vehicles had muzzle breaks to reduce recoil distance so as to reduce turret space/diameter.

Lewis

[Trooper]

Lewis, you really ought to go have a look at Tanknet.org where I asked pretty much the same question. The Abrams unit I was visiting last month was doing its last shoot with the 105mm rifles on the IPM1 before converting to M1A1, and I noticed that they were shooting APFSDS. It struck me as a bit incongruous, but there you go. (I have heard of rollers being used to counter-act the spinning effect, but apparently this round uses a copper band..)

NTM

[:USERNAME:]

I am sure the 105 uses sabot ammo. What i am saying is that it is more expensive to manufacture and is susceptible to quality problems.

When the spinning projectile leaves the tube and the discarding sabots sluff off, they can impart a slight disturbance to the penetrator. In a smoothbore they peel backwards and the penetrator is literally a dart.

Most nations realize the better performance and less expensive maintenance and cheaper ammo/tubes of smoothbores. The US is upgrading the 120mm to a longer L55 weapon soon i believe. I believe the US should keep 105mm Abrams around just do to the fact they can carry WP and other rounds the later version 120mm cant.

Lewis