Hi everyone! I’m back.
I just look to the muzzle break question thread ( http://www.finescale.com/fsm/community/forum/topic.asp?TOPIC_ID=51425 ) and a question popped in my head:
Why does some modern AFV sport a rifled cannon and others a smooth-bore one?
My guees is it has to do with the ability to fire missiles through the cannon or maybe one is significantly cheaper.
One thing’s for shure at least someone in this forum knows the answer [:)]
I believe that the smoothbore gives up some on accuracy, but you gain on muzzle velocity.
Both are accurate and neither is less expensive. It is just two differant ways to do it. Neither is better or worse the the other. They take different projectiles. Smooth-bores have to have fin stabalised projectiles to maintain stability, where a rifled cannon uses standard rounds that are stabalised by spining them like a football. It basically comes doen to the preferance of the maker and buyer.
Example:
British Challenger tank is rifled and is just as accurate and lethal as the US M1A1 tank which is smooth-bored. Both have 120mm cannons.
Is it just me or is the arrow-like projectile the M1 fires is really cool? I never realized until about a year ago (when I started on armor) that the “shell” was really a sabot (sp?), and the real projectile was like… the tip of an airbrush! Only bigger! I always wondered why M1 ammo always had that wierd pointy thing at the top…
[:O] I thought riffled were more accurate. Maybe I was wrong assuming riffled ones suffer more wear.
So you could fire a missile through a riffled cannon?
Can’t recall if it’s rifled, but the 152mm gun on the M-551 Sheridan could fire both conventional rounds and missiles.
I’d like to see that! That would be cool.
It was, indeed, rifled; but it had a special straight groove along the barrel to keep the missiles from spinning.
Anyway, about “rifled vs smooth”…
Rifled barrels are superior for traditional ammunition (you know, the stuff that looks like big rifle bullets)
Smoothbores are superior for HEAT and APFSDS ammo.
Reasons for this?
-fins cause a lot of drag, so it’s better to stabilise a projectile by spinning it if possible.
-spin stabilization is bad for HEAT, because it destabilizes the jet, reducing penetration; and it simply doesn’t work for APFSDS, because after a certain lenght/diameter ratio, centrifugal force becomes stronger than the stabilizing effect, and the projectile turns sideways.
Using HEAT or APFSDS out of a rifled barrel is possible, using rotating driving bands, but this makes the ammo more expensive (and in the case of HEAT, it takes away space that could contain explosives).
The Brits use rifled barrels because they assumed, a long time ago, that simple APDS and HESH (a.k.a. HEP) would be enough to defeat any enemy vehicles; this turned out to be wrong but the added cost for making APFSDS ammo with driving bands appears to be less than switching to smoothbores.
edit: whoops, frogot the end of the post…
Generally, unless you have some special reason to favor one over the other, you’ll use smooth or rfiled according to the need - an MBT will need a lot of high-penetrating ammunition (i.e., HEAT and APFSDS), so smoothbore is the choice; an SPG will mostly fire HE or cluster munitions (which often rely on spin to properly separate), so it’ll get a rifled tube; etc.
WOW! Thanks for the information.
I knew this was the right place to ask.
what about longevity
Sorry, none of my trustworthy sources talk about the relative service life of smooth vs rifled barrels; only how different ammo types cause different amounts of wear.
And my untrustworthy sources give conflicting information.
The way I’ve looked at it, the smoothbore allows a better job of armour-piercing, either through KE or HEAT. The problem is that you are reduced in the variety of ammunition that you can shoot effectively. For example, the HE content of a rifled HE round is higher than that of one from a smoothbore. According to the Tanknetters, it’s a combination of shell wall thickness, and the need to leave room for the fins. Not a problem where the rifle is concerned. The Swedish have come up with a make-shift HE round using a converted mortar bomb.
FWIW, the rifle currently has the tank-on-tank kill distance record, of 5,300m in 1991.
The British tankies are extremely unhappy at their forthcoming move to smoothbore from rifle. They love HESH. Frankly, given the conversion is going to cost akin to 2.5 million pound per tank ($3.5m), it is astounding that they decided that converting 380 tanks would be cheaper than keeping the ammunition facility open.
NTM
No more rifled bore for tanks …
Since I worked in the field for sixteen years, and crewed tanks for eight years prior to that, I’ll offer my 2 cents:
Smoothbore weapons are indeed cheaper to manufacture, and offer longer service life. Cutting lands and grooves into a gun tube requires specialized tooling, and requires higher quality steel to prevent flaws in the material which would cause failure. The very nature of rifling creates “stress risers” that promote cracking. A smoothbore design eliminates all of this. Rifled designs needed intense monitoring (borescoping) during thier service life to monitor cracking and metal fatigue caused by dynamic stress.
That being said, the cost savings are offset by the ammunition required for the smoothbore. Fin stabilized ammunition is more complicated in it’s design, requires a mechanism for the stabilizers to deploy, thereby being much more expensive than rifled tube ammunition.
Initially, the smoothbore tube, being manufactured with lower carbon content, was found to loose zero with regularity, especially when subjected to rapid fire with the high pressure sabot ammunition. Enter the MRS. Hence the beginning of the myth that the smoothbore was inaccurate.
Accuracy on par with rifled designs was acheived by the development of the Muzzle Reference System. Simply, an illuminated reticle attached to the end of the tube, which would compensate for the “flexing” characteristic observed during firing, when the heat and friction would cause the tube to loose zero. The gunner now has the ability to re-affirm zero in between engagements, by simply re-calibrating the primary sight reticle with a toggle switch.
When a projectile is fired, although not visible to the naked eye, the gun tube reacts as if it were a plucked banjo string, resonant vibration and micro “flexing” will occur. At the molecular level, the structure of the steel is affected. Depending on the chemistry and volume of certain elements in the steel, and how they react to heat induced by friction, so goes the accuracy potential of the weapon.
The MRS, coupled with advances in fire control computer processing and improved ancillary sensors, such as crosswind, cant, ammo temperature, etc. have vastly improved the ballistic solution and targeting capability of the MBT today.
Ammunition quality is crucial to the success of the smoothbore design. Rheinmetal has pioneered fin stabilized ammunition development, and as a consequence, virtually all Western MBT’s to include the LeClerc, use the system and license the ammunition design with variation. The exception are the Brits.
After leading the pack with the development of the rifled 105mm Vickers tank gun, and later the 120mm design, investing three decades of R&D and metallurgical innovation, the rifled weapons are hard to give up on for the English. The latest milestone was the inclusion of polygonal rifling which has too many benefits to list here.
Personally, having fired both types of weapons, with multiple types of ammunition, across a wide variety of tanks and fire control systems, I would still prefer a rifled main gun, probably because I am old fashioned. The battle proven weapons need no further endorsement.
When you see a 105mm break a 2x4 range marker at 2000 meters, it is an enlightening and life changing experience for a young tanker.
Steve
with what crockett said the smooth bore being cheaper to make and basically easier as well then why 3.5 mil usd per tank on a a barrel
sounds a bit like the brits have the us government $500.00 hammer syndrome too lol
The glitch with that argument is that the first example I can find of an in-service MRS is on a rifle. More specifically, the L11 on the Chieftain Mk5 of the early/mid 1970s. It then started showing up pretty much on anything after that, either the 105mm rifles on Leopards and M1s et al, or the smoothbore 120s.
I think mainly the reputation for inaccuracy from the smoothbores really just dates back to ye olden dayes of musketry, when the rifles that were introduced were so much more accurate, that nobody really bothered to consider the possibility of modifying ammunition for smoothbore use because ‘everyone knew’ that rifles were better.
The battle proven weapons need no further endorsement.
I’m a fan of the rifle myself, at least the 120mm version, but aren’t longbows and M14s battle proven? Nothing wrong with embracing new developments, after all!
NTM
Just because rifled suffer less deformation doesn’t mean it doesn’t need the MRS.
Nice to get info from an actual expert… however, this:
sounds rather strange, considering that most fin stabilized ammo I’m aware of uses fixed stabilisers…
Plus, as outlined above, some ammo types require fin stabilization, and adapting them for rifled weapons makes them even more expensive.
I was referrring to latest generation development namely XM578, pictured below in the top frame fins deployed.
MRS was deployed on the XM1 in 1977, the inference was not that it was solely developed for the smoothbore, but that it is vital to maintaining accuracy on par with rifled tubes.
Also, check out this interesting link on the future of DU projectiles in the British Army…
http://www.nukewatch.com/du/20030921telegraph.html
and a related Robert Fisk article:
http://www.robert-fisk.com/articles22.htm
There seems to be a misunderstanding surrounding the function of SABOT in rifled and smoothbore tubes…this will clarify…
http://www.answers.com/topic/kinetic-energy-penetrator
Ah, so you took a rather unusual feature, which happens to be present on one type of round you happen to be familiar with, and put it in your post as if it were standard.
Got it.
Nothing I didn’t know already; no misunderstanding here.
What gave you the idea?