I noticed in doing some searching on a recent question here, that the Abrams has a 120mm smoothbore gun, while its counterpart in the British Army, the Challenger 2, has a 120mm rifled gun.
Now, I am well aware of what the terms mean in the conventional sense, but what’s the difference operationally between the two ? Is one ‘better’ than the other ? What are the pro’s and cons of each, such that the Abrams is smooth while the Challenger is rifled ?
Not a gun expert here, but IIRC, it has to do with the types of projectiles being fired from the guns. I think that the reason the US military has smooth bore barrels is so that they can stuff a wider variety of shell types in the barrel, whereas the Brits tend to only use one kind of shell.
All other things being equal, a rifled gun will fire a projectile more accurately and with greater range, but at a somewhat lower velocity, because the rifling actually carves grooves into the projectile as it travels down the barrel. The spin imparted to the projectile gives it better aerodynamic properties, but the lower velocity means less energy is delivered to the target by momentum.
However, the main source of a tank round’s damage is its explosive charge, not its momentum. The two basic types are high explosive and armor piercing, and there are lots of variations.
Rifled barrels for guns/artillery/cannon/etc allows the shells/bullets/balls to fly farther and more accurately because a spin is applied to the projectile, so hypotheically, the challenger shots will go farther and hit more often then abrams shots.
The disadvatages of rifling a barrel is that it makes it slightly harder to clean and it makes it much harder to load a projectile from the muzzle(the end the shot comes out of) end (try ramming a shot into a rifled muzzleloading rifle and you’ll see exactly what I mean).One of the reasons that rifles were not used much during the revolutionary war because it took far longer to reload a rifle then a musket. Of course, this is rather a moot point since most (if not all)military arms have been breechloaded(loaded from the trigger end of the rifle) since the mid 1800’s.
However, I’ve heard the US Army has a way to compenstate for the smoothbore guns, so in that case, it probably wouldn’t matter much.
Projectiles fired from modern smoothbores are fin-stabilized, which provides the same benefits to accuracy as the spin imparted by rifling.
AntiTank shells kill by sheer kentic punch or by chemical action (an explosion)
Kenetic rounds depend on lots and lots of speed and a very hard & heavy dart, a depleted uranium penitrator. These rounds need a rifled gun (a “rifle”).
Explosive rounds use a High Explosive AntiTank Warhead. This makes a directional explosion by use of a lined shaped charge. These rounds prefer to not be sppinning. (You really don’t want to know why.) Further they do not need to be going very fast. These rounds tend to have larger diameters and use fins to keep them straight in flight.
Is that enough or do you eed more?
Actually, I’d like to know why the high explosive rounds don’t spin.
Also, what is the difference between HEAP and HEAT shells? Different shaped charges?
OK… You asked for it…
A HEP (High Explosive Plastic) round is called a HESH (High Explosive Squash Head) in British service. Same thing. This thing gobsmacks the target and makes a big puddle of explosive silly putty ™ in the armored surface.
In two shakes of a lambs tail the fuse sets off the charge, which is contact with a large patch of the target’s surface. The surface flexs (or clangs like a bell if yo prefer) and releases flaks of spall. Of course these flakes are red hot, razor-sharp and moving very fast.
They will turn a crew into a long-division problem. This round is medium-good against tanks (for some technical reasons) and real good against concrete bunkers.
A HEAT (High Explosive Shaped Charge) round uses a different technique.
Let’s begine by telling you how to make one. Go to the store and get a couple of kilos of platic high explosive. Got it? Good. Fill a coffee can with the stuff. Take a wine bottle and squish the explosive so there is wine-bottle-neck-shaped cavity in the explive. Line the cavity with cold-pressed stell a couple of mm thick (this is optinal).
Now put your detonator at the OTHER (flat) end of the charge. No ignite the charge and watch the explosion closely. (And darn quickly.) The detonator goes off and so does a thin disc of explovie on the ass-end of the charge. The explosion travels through the charge until it get to the cavity.
Now look carefully, see how the explosion moves through the air (in the caivtry) FASTER than the explosion still in the explovie? OK, that means as the explosion moves through the chage the tippy-tip (to use the technical term) of the explosion gets further and further ahead of the rest of the explosive force.
This tippy-tip is very powerful as much of the explosive force is contained in it (the force wants to move in the fastest way it can).
As a result the HEAT round “burns” a smallish hole through the armor. It will also go right through your uniform, you don’t want to be there when it happens.
OK, now as to your question.
If the HEAT round spins, the explosive jet tends to deform, loosing focus on the target.
Guns that shoot sabot (don’t ask) tend to be rifled, guns that shoot HEP and HEAT tend to be smooth.
OK?
The latest armor piercing shell for the Abrams is the M829AE3 It is a discarded sabot, kinetic energy round. Basically, it’s a depleted uranium arrow (fin stabilized) surrounded by a sabot (the hourgless shaped piece in the picture) which is a case to fit the arrow inside the 120mm gun. Soon after it’s fired, the sabot falls away leaving only the arrow to fly towards the target. It relies entirely on the high speed, density, and hardness of the projectile to pierce armor. Anything that will slow it down, like rifling, will reduce its effectiveness.
Yes, and in the same way, some HEAT rounds (protected from spinning by a rotating collar) are fired from rifled guns.
But still most KE shells are fired from rifles and most CE rounds from smoothbores.
There’s something wrong here. If a kinetic round needs max speed, it needs (optimally) to be fired by a smoothbore, not a rifle.
If a HEAT round needs NOT to be spinning, then again it needs (optimally) a smoothbore gun. In you stuck on fins to counteract rifling, I think you’d seriously fuck up the stability of the round.
I’ll do some searching around and see what I can find.
The main difference that I can see in the rounds employed by each tank, is that the Challenger does not use HEAT, and the Abrams does not use HESH.
Both use KE rounds (APFSDS - just called ‘fin’ by British tankers). Both also use Depleted Uranium rounds which seem to be listed as a separate type.
I
In my Army days, we were told that two reasons for the introduction of the smoothbore MBT gun (after the sabot became the primary anti-armour round) was ease of maintenance and reduction of barrel wear, both of which sound quite plausible to me.
(The HEAT (Danish abb.: HULA) rounds for our 84mm recoilless rifles used fancy teflon bearings to prevent the barrel rifling from introducing too much spin on the projectile. Nice weapon, but you needed a Ph. D. in math to figure out where to aim it.)
A small nitpick. Shaped charges don’t burn through the materials against which they’re placed, be it armor or structural members in a building demolition. The charge pushes the charge’s lining through the material. Steel has a yield strength around 50,00 psi and the focused blast exceeds this. Needless to say the material being shoved aside so rudely tends to be white hot, but the shaped charge does not vaporize it, as I have so often heard mis-explained.
Yes, I know.
The Carl Gustav? Gee, what is with that blinking light in the sight?
Yup, the Carl Gustav.
The only “blinking light” sight I’ve seen was a (retrofitted) attempt to give the gunner a sporting chance of actually hitting a moving target.
The idea was having a light blink at intervals equal to the flight time of the shell. The gunner can then estimate the target’s lateral movement across the crosshairs between two blinks - that is the distance he needs to move his aimpoint in front of the target. With a bit of luck, the shell will then finish its trajectory in the general vicinity of the target, at least. Neat idea, but I’ve no idea of how well it holds up in battle.
Tank guns typically fire 3 types of projectiles. Each is affected differently by rifled v.s. smoothbore barrels, and the choice of which barrel type to use is a trade-off based on what the gun designer/military user sees as most important. The 3 projectile types are:
**APFSDS (Armour Piercing Fin Stabilised Discarding Sabot ** - This type of projectile is a long thin rod of metal with small fins at the end, inserted into a sabot which is the same diameter as the inside of the gun barrel. When fired, the propusion charge pushes against the base of the sabot and propels the projectile out of the gun, where the sabot falls off, leaving the center penetrator rod to continue on and hit the target. This is the projectile generally used against other tanks. It does not explode (although the target might!).
This type of projectile is most accurate when it doesn’t spin, so can easily be used in a smoothbore. If fired from a rifled gun, the sabot needs to have some sort of ball bearing collar or other mechanism added to allow it to spin while preventing the penetrator rod from spinning, making it more complex and expensive. (You may lose some accuracy at long ranges anyway, as it is difficult to prevent some spin. OTOH the spin ensures that the sabot is less likely to separate unevenly and defelect the penetrator rod, which is sometimes a problem with non-spinning sabots.)
Deleted uranium is used by the US in current M1 APFSDS projectiles as it is dense, stiff, and can get hot enough to ignite due to friction when penetrating the target armour, all desireable features.
HEAT (High Explosive Anti-Tank) and HEP/HESH - There is a trade-off with this projectile, as it is more accurate when fired from a rifled gun but more effective when it hits if fired from a smoothbore. It needs a non-spin collar or other mechanism similar to APFSDS sabots if you want to get the best effect on the target after firing it from a rifled gun. HEAT is the projectile generally used against APCs and other lightly armoured vehicles (APFSDS is too powerful for these targets, and can go right through and out the other side with little damage in some cases). As explained by Paul in Saudi, these explode, but in a very controlled fashion.
HE (High Explosive - This is the basic “exploding” shell used by artillery, WW2 tanks, and Hollywood. It is most accurate when fired from a rifled gun and is much less accurate when fired from an unrifled gun. HE is used against infantry, buildings, etc.
If you expect your tank to be mostly shooting at enemy tanks using APFSDS, with other targets handled by other weapons (such as artillery), then a smoothbore gun is a good choice, as it is cheaper to manufacture, doesn’t wear out as fast, and is easier to clean and maintain.
If you expect your tank to need to do a significant amount of shooting at things other than tanks, a rifled gun is a good choice, as it provides greater accuracy with a range of different projectiles, at the cost of some extra complexity and expense.