I’m not sure there is an actual factual answer to this rather than opinion…
The Challenger 2, and I think pretty much every post-war British tank, has had a rifled main gun. The Leopard 2, M1-A1Abrams, LeClerc, Merkava, Chinese Type 99, T-90 and I think pretty much every other major tank has a smoothbore main gun.
Why are the British different on this?
Seems the Challenger 2 is getting a smoothbore gun.
I am guessing they dragged their heels since you need to manufacture new ammo. Might have wanted to keep the rifled barrel longer to go through some stocked ammunition rather than throwing it out. Dunno though.
Another factor in the late retention of rifled guns is that the Royal Army favored a type of anti-tank round called the High-Explosive Squash Head. Instead of punching its way through enemy armor, it squishes a pat of explosive up against the outside and then explodes, causing high-speed fragments to be ejected from the inside wall of the enemy tank. It works best against homogeneous armor and not so well against modern laminated armors. This round has no fins, but is spin-stabilized like most rounds from small arms to artillery, so it needs a rifled barrel.
It was the improvement program that made me start wondering why they had stayed rifled for so long…
The round thing seems to make sense, but it just surprises me that the choice is so overwhelmingly the other way - does no one else like HESH rounds? Or does the British Army have a different vision of the use of armour in combat?
I’d just think that if this was a debatable issue (which one is better), then there would be more of a split but it seems every other major manufacturer uses smoothbore.
Considering the widespread use of Reactive Armor perhaps the utility of HESH rounds is a lot less than in the past?
For smoothbore MBT ammo, how do they get stability on non-saboted rounds, like HEAT or HEP? Or do HEP rounds used in smoothbores have fins too? Hard to kill dismounts with sabot rounds, though I suppose that’s what the coax is for…
Bear Nenno, where are you…?
HEP rounds are basically a British weapon. In the US Army they are only used on the M135 165 mm short-barrelled demolition gun carried on the M728 Combat Engineer Vehicle. This is a rifled gun.
The HEAT round for the M1 Abrams is a fin-stabilized sub-caliber round that uses a sabot, much like the APFSDS round. See the cutaway towards the bottom of that page.
For dismounts, the Abrams uses the canister round, essentially turning the tank into a 120mm shotgun, no need for stabilization.
What are the advantages of the smooth-bore guns?
Cannon (smooth-bore guns) do not spin the projectile. This reduces accuracy but allows you to use chemical-energy rounds (Canister as well as HEAT and HESH). A rifle spins the projectile, this means they are best for rounds that use kinetic-energy as a killing mechanism.
Does that help?
What’s the problem with spinning chemical-energy rounds?
? Pretty sure Sabot rounds are fired out of a cannon. After the sabot drops off, the projectiles fins spin it. These are kinetic-energy weopons like depleted U.
Chemical-energy rounds would wear out a rifled barrel much more quickly (like, within 500 firings).
I’ve always assumed smooth-bore guns to have a higher muzzle velocity, as the twists in a rifled barrel would necessarily induce more drag. Wouldn’t this actually make smooth-bores a more suited design for kinetic-energy rounds? (Of course, to not lose accuracy one would have to deploy fins to stabilize the round, perhaps the increased drag would offset the muzzle velocity advantage?)
The spin disrupts the plasma burn-through that makes the round work in the first place.
[quote=“paperbackwriter, post:7, topic:549303”]
Wow. That’s … cold. Do Abrams loaders customarily ask the tank commander if he’d care to give the enemy a whiff of the grape?
[quote=“Mr.Excellent, post:15, topic:549303”]
No, but they do say, “I am about to drop the Hammer, and dispense some eeendiscriminate Justeeece!”
Think you’re right about the spin, but I can’t resist nitpicking “plasma burn-through”. The HEAT round shaped charge doesn’t make plasma, or even a “jet” - the liner is SOLID as it punches through the armour. This has been proven by flash x-ray diffraction. (It does behave approximately as a Newtonian liquid during the explosion because the stresses on it from the shaping explosive are far above its shear strength.)
Man, everything I wanted to come into this thread and say has already been said. 
You’re correct - the classic KE armour penetrator is a long thin needle of something dense like DU or tungsten, fin stabilised, with a sabot to make up the calibre, fired at a hell of velocity. The fins just keep it going straight - they don’t add spin. And ideally you fire them out of an unrifled gun. There are some designs that let you fire fin stabilised penetrators from a rifled gun though - sabots with spinning sleeves or bearings between the sabot and penetrator, etc.
HEAT rounds shouldn’t be spun as it reduces their effectiveness. Fairly sure there’s also some cunning sleeved shell designs that let you fire HEAT from rifled barrels without them spinning. I think HESH is indifferent to spin.
With tank guns there’s two ways to go: 1) the slightly more accurate rifled gun, which can shoot HESH and other HE rounds, but needs specialised shells to shoot non-spinning HEAT and KE penetrators, or 2) the less accurate smoothbore gun that shoots HEAT and HE penetrators with ease,but needs fin stabilisation or shells with tails to shoot e.g. HESH or smoke. Competing technologies, and the smoothbore seems to have won.
Can’t see why that would be the case, except possibly with cannister. Saboted KE penetrators wear out even smoothbore barrels fairly quickly in any event, just because the muzzle velocity is so high.
That’s just the point: even if you can only fire twice as many rounds before replacing an unrifled barrel, it’s still twice as many.
