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When Smoothbore is Superior to Rifling.

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When Smoothbore is Superior to Rifling.

Unread postAuthor: boyntonstu » Mon Nov 02, 2009 8:52 pm

When Smoothbore is Superior to Rifling.

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; a practice that has been taken up by Israel—a major supplier of "arrow" rounds[citation needed]—China, France, Pakistan, Germany, Soviet Union/Russia and the United States in their tanks. APFSDS can still be fired from rifled guns but the sabot is of a modified design incorporating bearings to isolate the spin of the sabot in the barrel from the round itself, so far as practicable. Rifled guns have been kept in use by some nations (the UK and India, for example) because they are able to fire other ammunition such as HESH rounds with greater accuracy. However, the rifling wears down under regular APFSDS use and requires more maintenance. For these reasons the British Challenger 2 is being trialled with a Rheinmetall 120mm smoothbore gun.

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

You learn something new every day!

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Unread postAuthor: D_Hall » Mon Nov 02, 2009 9:06 pm

Welcome to 1980.

But if you really want to bake your noodle, there are also NON-discarding sabot rounds out there. Voila, your penetrator can be 10X as long as it is in diameter (or whatever) but your overall projectile L/D stays reasonable as the sabot flies with the penetrator all the way to impact (and then gets stripped by the impact itself). Note that these are very popular with airborne systems as jet engines don't like injesting discarded sabots.

Also, the Ruskies like smoothbores because they make good rocket launchers (example: BMP-2).
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Unread postAuthor: POLAND_SPUD » Mon Nov 02, 2009 9:30 pm

@D_Hall
I think you meant BMP-3,
The main arment of BMP-2 is just a 30mm auto-cannon
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Unread postAuthor: D_Hall » Mon Nov 02, 2009 9:41 pm

Ack. Correct. BMP-3. I guess that's what I get for going off of memory.
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Unread postAuthor: hi » Mon Nov 02, 2009 10:24 pm

its also superior when you are an 17th century soldier in the infantry and there the cavalry is charging at you... you can load a little bit faster.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 02, 2009 11:08 pm

D_Hall wrote:But if you really want to bake your noodle, there are also NON-discarding sabot rounds out there. Voila, your penetrator can be 10X as long as it is in diameter (or whatever) but your overall projectile L/D stays reasonable as the sabot flies with the penetrator all the way to impact (and then gets stripped by the impact itself). Note that these are very popular with airborne systems as jet engines don't like injesting discarded sabots.


The problem with such projectiles is that the aerodynamic advantage of a discarding sabot is negated. Many APCR (HVAP to you folks across the pond) shells also have a lower weight than the equivalent solid shot, which might give them a higher muzzle velocity and better penetration close up but this effect tapers off considerably with range.

As you mention though for airborne guns it is undesirable to have sabots flying off that may be sucked into engines, the PGU-14/B round fired by the A-10 is certainly a case in point - though for example a side-firing AC-130 gunship would not have such difficulties.

Also, the Ruskies like smoothbores because they make good rocket launchers (example: BMP-2).


Not necessarily, your M551 has a rifled barrel and is perfectly happy to fire the Shillelagh missile :)

All western powers have moved to smoothbores for their main battle tank guns, mostly for velocity reasons. The British were the most stubborn, arguing that conventional high explosive shells from a rifled barrel were more accurate than the finned full calibre rounds fired from smoothbores, but the velocity advantage is too big to ignore.

hi wrote:its also superior when you are an 17th century soldier in the infantry and there the cavalry is charging at you... you can load a little bit faster.


If you have spherical lead, somewhat, however the introduction of the Minie ball roundwhich expanded on firing meant that it could be made slightly below the calibre for easy muzzle loading and still keep a good seal.
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Unread postAuthor: Hotwired » Tue Nov 03, 2009 9:45 am

jackssmirkingrevenge wrote:All western powers have moved to smoothbores for their main battle tank guns, mostly for velocity reasons. The British were the most stubborn, arguing that conventional high explosive shells from a rifled barrel were more accurate than the finned full calibre rounds fired from smoothbores, but the velocity advantage is too big to ignore.

Velocity or long range demolition charge placement.

Maybe when someone gets round to fielding tanks against tanks again this might be useful.

Until then just the reduced wear on barrels.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 03, 2009 10:55 pm

Hotwired wrote:Velocity or long range demolition charge placement.


As pointed out in your link:

From the 1970s onwards, tank armour design has tended towards layered composites of hard metal and heat-resistant materials. This type of armour is a poor conductor of the shock wave, and furthermore "spall liners", made of materials such as Kevlar, are commonly fitted to the interior surface of the armour, where it acts to retain any spall that does occur.


APFSDS really is the only reliable way to knock out a tank on the modern battlefield. Ironically though, there is only one recorded case of a Challenger being destroyed in combat, and it was by friendly fire using HESH rounds.

Maybe when someone gets round to fielding tanks against tanks again this might be useful.


There was plenty of tank versus tank combat in Iraq, and the 120mm APFSDS (coupled with superior sighting and communication equipment) made sure the battles fairly one sided.

The extended range of DU penetrators combined with the highly accurate fire control system and gun of the M1A1 provided American tanks with a considerable advantage over their Iraqi counterparts. While Iraqi T-72 tanks had an effective firing range of under 2,000 meters, U.S. tanks had an effective firing range of approximately 3,000 meters. In one case, the frontal armor of a T-72 was penetrated by a 3,500 meter shot (over 2 miles) from an M1A1. But the longest confirmed kill of the war was by a British Challenger tank, which destroyed an Iraqi tank with a DU round over a distance of 5,100 meters (over 3 miles). Even over these extended ranges, the DU rounds proved highly effective in penetrating Iraqi tank armor. In one case, a DU round "hit the turret of a Russian-made Iraqi T-72 tank, passed completely through the turret, and hit (and destroyed) a second T-72."


Another point to make about the advantage of smoothbores is that shaped charge rounds lose some of their effect if fired from a rifled barrel, because the centrifugal force tends to disperse the hot jet of gases and molten metal that the round relies on for effect.

Oh, and let's face it, most shotguns are smoothbores :D
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Unread postAuthor: D_Hall » Tue Nov 03, 2009 11:11 pm

jackssmirkingrevenge wrote:APFSDS really is the only reliable way to knock out a tank on the modern battlefield.


Huh???

While it isn't fired from another tank, please show me ONE instance of a tank EVER surviving a hit from a Maverick. Not that I'm a huge fan of the Mav, but it sure as hell is reliable from a kill perspective(*). My point not being that the Mav is some sort of end-all be-all but rather there are plenty of ways to reliably kill tanks. They just don't all come out of the barrel of a gun.




(*) Primarily because it was not designed as a tank killer. It was intended as a bunker buster (when bunkers were way softer). Result? To say that Maverick is capable of killing a tank is like sayign that a sledge hammer is capable of driving a nail. Uh... Yeah, it can do it. It's overkill! Hell, just the airframe alone is quite the projectile. I've seen photos of M-109 Paladins with holes clean through them that were made by Mavericks that didn't even have warheads on them. 300+ pounds moving at transonic speeds packs one hell of a punch all by itself. Throw a 100+ pound shape charge into the mix? Add to that the fact that it's attacking from the top? Again... Overkill.
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Last edited by D_Hall on Tue Nov 03, 2009 11:25 pm, edited 1 time in total.
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Unread postAuthor: Solar » Tue Nov 03, 2009 11:19 pm

I read somewhere recently that a finned projectile would be less accurate if any spin was induced on it whether rifling induced or otherwise. Is this accurate? So only spin if no fins?
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 03, 2009 11:25 pm

I should have qualified my statement, APFSDS really is the only reliable way for a tank to knock out another tank on the modern battlefield.

Hell, just the airframe alone is quite the projectile. I've seen photos of M-109 Paladins with holes clean through them that were made by Mavericks that didn't even have warheads on them. 300+ pounds moving at transonic speeds packs one hell of a punch all by itself.


That much I believe, sometimes you don't need explosives :)
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Unread postAuthor: D_Hall » Tue Nov 03, 2009 11:38 pm

Solar wrote:I read somewhere recently that a finned projectile would be less accurate if any spin was induced on it whether rifling induced or otherwise. Is this accurate? So only spin if no fins?

Spinning seems to work well for arrows.

I can only imagine that the bigger issue is that fin cants mean more drag and therefore less range. So while a spinning projectile may (or may not?) be more accurate (it is for arrows), it may not be worth it for kinetic reasons.
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Unread postAuthor: Hotwired » Wed Nov 04, 2009 12:02 am

I'm wondering, with so much focus against protection from HEAT and APFSDS which if unguarded against are pretty fatal to a MBT and for the same reason are incredibly popular....

...how modern composite armour and even active armour would stand up to a full calibre AP shell. A much more massive projectile with considerably less subtlety in its effects.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 04, 2009 12:19 am

Hotwired wrote:I'm wondering how modern composite armour and even active armour would stand up to a full calibre AP shell. A much more massive projectile with considerably less subtlety in its effects.


If an inert 2,000 lb lump of concrete at subsonic speed it capable of knocking out a tank, I have no doubt the effects of full calibre 120mm steel shot at several times the speed of sound would be pretty terminal, even if perhaps the round would not actually penetrate the armour.

It's worth nothing that a direct hit from a conventional large calibre HE shell is also enough to disable a tank, again the crew might be safe inside but the tank's ability to move and fight would be removed.

I suppose the great advantage of APFSDS is its high muzzle velocity and exceptionally good ballistic coefficient. The flat trajectory makes it easier to fire accurately and indeed some of the kills achieved in modern tank combat are at incredible ranges, I believe the current record for APFSDS is 5.1km (by a Challenger 1 with a rifled barrel :roll: :D )
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Unread postAuthor: ThegunGuy » Fri Nov 20, 2009 12:39 pm

Is this thread to old for this post?
I think that it would be far more efficient to just drop a beer bottle full of gasoline, polystyrene and white phosphorus onto the air intake than to spend a half a million dollar bomb blowing up a ten million dollar tank, it doesn't take to long for someone to surrender in those conditions. replace the beer bottle with an aluminum can and put fins on it and you have a real monster. Just saying modern military spends to much on complicated solutions to problems that have much more simple answers.
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