Rifled vs Smoothbore Barrels

Discussion in 'RAC' started by Ignorant_Layman, Apr 25, 2011.

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  1. This is a debate I've stumbled across here a few times. From what I can gather, smoothbore seems to have won the argument insofar as Challengers (the only big name tanks which were still using rifled barrels?) are now being fitted with smoothbores, but a fair few people continue to defend the rifled barrel, citing HESH capability and a particularly long range kill achieved with a rifled barrel once during the Gulf War.

    I must confess my personal knowledge of the subject is very cursory, coming largely from forum searches and checking out "ra ra" videos such as the following:


    (Skip to 1:50)

    Could someone more in the know explain the debate? If rifled barrels really do have better range and accuracy, why the primacy of the smoothbore? Is losing HESH (high explosive squash head?) really that big of a deal, and was it primarily an anti-armour round (as described above) or a round for use against fixed positions (as I've read elsewhere)? Is it true that it's much hader to use autoloaders with a rifled system? Is it all just a question of cost and going with what's more mainstream and has the spares and upgrades which are easier to get hold of?

  2. First of all, the idea of fitting CR2 with a smoothbore gun has been dropped. This is down to funding. Smoothbore guns have less barrel wear and can provide higher muzzle velocity meaning greater penetration for armour piercing rounds. The UK has been against smoothbore in the past because initially only anti armour ammunition was available, meaning lack of flexibility and tanks being only mobile A/T guns. Also there were claims that accuracy suffered at longer ranges. The fact that the UK led the world in the design of rifled tank guns may have had a lot to do with it as well.

    Things have changed. New ammunition of various types has been developed for smoothbore, so the old argument about HESH being vital is now dead. HESH is a dual role shell but it's value as an anti armour round is now virtually zero, most modern tanks would survive a hit from HESH. The main point today is that because of the introduction of new tank armour such as Chobham/Dorchester ect, current rifled & smoothbore guns/ammo may soon be unable to deal with the most modern tanks. The rifled barrel has been developed as far as it can be without a complete rethink and much financial input. Smoothbore guns will be easier to improve and the higher muzzle velocities needed to penetrate future armour easier to obtain.

    The spectre of British tank crews seeing their shells bouncing off the enemy's tanks in battle could soon return. It is unlikely that a new rifled tank gun will ever be developed. The current rifled gun the L30, together with DU armour piercing rounds is as good as anything in the world, "today", but tomorrow belongs to smoothbore.
  3. Good post - I think you summed up what I was trying to say on another thread!

    Our enthusiasm for rifled barrels and HESH has an awful lot to do with our own history in tank gun development, and unfortunately a bit of NIH syndrome - which seems to pervade research establishments worldwide.
  4. Perhaps the needs to be taken back a stage further. It is important to understand why we need or don't need rifling at all and this hinges on projectile stability in flight.

    In essence, in order to ensure that a projectile remains accurate and strikes the target front end on (as opposed to tumbling in flight and striking the target side on or rear on) the projectile needs some sort of stabilisation to counteract the effects of gravity and aerodynamics in flight. There are two ways this is commonly achieved: the first is by spinning the projectile along it's axis delivering stability on the same principle as a child's spinning top or gyroscope. The second way is to rely on aerodynamic stability using fins to keep the projectile aligned to the target, like the fins on a dart as it is thrown toward a dartboard. If a projectile is fin stabilised, clearly it does not spin in flight (or may spin slowly).

    In order to fire a fin stabilised projectile through a rifled barrel, it must be fitted with slipping driving bands in order that the driving bands rotate in the barrel but the projectile does not (or not too much).

    A bit more to follow when I next have time.
  5. It's all purely academic. The UK now has no production facilities for the rifled tank gun or it's ammunition, and that has been the case for a while. Industry was not prepared to fund factories to sit idle in case the MoD might one day place a small order for something no-one else uses, and neither was the MoD. The phrases "at risk", "capability holiday", "Defence Planning Assumptions" and so on no doubt figure in the justification.

    So, We either fit the NATO standard 120mm and buy ammo from one of the many manufacturers or we dump CR2 when the existing ammo goes out of life. (I'm assuming a switch to 125mm would be a step too far !)
  6. The downside of the finned ammo is that it leaves less 'room' for the cargo. If you compare the amount of HE in a Soviet 125mm finned round with the amount carried in a 120mm rifled round, you'll see the rifled round makes a bigger bang.

  7. ... although you could make a finned HESH round, but it would be pretty long, something like 80cm +.

    I think HESH or an equivalent blast round is still useful for smashing stuff up. It proved quite good in Iraq for taking out mudbrick etc. They even found that SHPrac was useful for giving a graduated response - something like a top end donk gun! Darts and HEAT seem to be particularly useless at this type of task - they only punch fist size holes in things and darts create a 7km downrange hazard. We need to remember that tanks are not just anti tank weapons. Although this is the prime role, in many cases tanks are used as mobile firebases that need to be able to defeat a range of targets..

    I wrote a piece about spin/drag for Arrsepedia a few years back..

    Ballistics etc - ARRSEpedia

    I think for tank guns, the smoothies have got the lead now, but this is not a cheap or technically easy path - barrels and ammunition are difficult to make and maintain.
  8. I prefer the rifled option, you can stop a finned round from spinning down a rifled bore with drive band bearings, but you can't fire conventional finnless rounds as accurately through a smoothbore. Why close down your options to kinetic weaponry, the old bulky chemical stuff has much to offer.

    A lobbed HESH round my not be the dogs bollocks against modern armour but it's mustard against a whole range of hardened bunkers, pits, nests and sangars. And after all the modern armour is mostly carried by our allies.

    Rifled HEAT rounds are still more accurate and effective against armour at longer ranges than are kinetic rounds.

    I wish they'd dust off the SSSHHHH gun, the big pokey stick tank gun designed yonks ago to combat "the next generation of tanks", you know, the one we know nothing about.
  9. That's true, but there are other alterntives to the big bucket of HE in Harry HESH.

    The US M830A1 MPAT round is probably more effective against dismounts in the open or light cover, due to the optimized fuzing and fragmentation effect - the trouble with HESH is that the sidewalls of the shell need to be maleable enough to cowpat on impact, which is not so good for fragmentation pattern. The M908 MPAT-OR (OR= obstacle reduction) is quite an effective round at destroying fortifications - its terminal effect is more like some of the rocket-launched anti-structure muntions out there.

    I think one thing Afghanistan has shown is that we probably need a greater range of rounds for the main gun (a 'smart' airburst fragmantation round would be ideal) in the future, and we're just not going to get those if we stick with the L30.
  10. Sorry to bang on, but sticking with the L30 is not an option. The factories are gone, you cannot buy spares, barrels or ammo any more. And the only credible replacement is 120mm - here is no money out there anywhere, not even in the US, to do anything else. The Russians keep muttering about their 152mm gun but that's the one they were thinking about in 1989 when the wall came down and they've done nothing remotely serious about it since then.

  11. That's what I was saying...I think?

    All the whizzy new rounds (like MPAT, M829A3 etc) are being made exclusively for 120mm smoothbore, which we will end up needing at some point. If we can't even produce any more L27, we have no hope of developing anything better.

    NATO briefly considered a flirtation with 140mm (I remember seeing the experimental rounds - your loader would need to be built ike Shrek!), but concluded that there was further mileage in 120mm (albeit smoothbore).
  12. I think you will find that smoothbores only require a shotgun licence. Rifled barrels a firearms licence which can take longer to get thus a longer wait for your tank which you would have to specify on your application before you buy it.

    Seriously though it has been mentioned that we do not retain the capability to manufacture rifled tank barrels. What about AS90 and naval 4.45 (114mm) barrels. Shurely they utalize the same engineering skills and tools and could easily be small order set up. We used to spit this stuff out like pins...
    • Like Like x 1
  13. I seem to recall reading a piece of (unclassified) work a year or so ago discussing tank ammunition natures and their relevance to the COE. Based on that and my own modest experience, I would suggest that the effectiveness of HESH against buildings and bunkers has been dramatically over-played. The sort of buildings we tend to fire against on current operations, made of mud-brick or thin block work, are often not sufficient to squash the round and make it function correctly. In addition, I would suggest that the current HESH round creates insufficient splinter to be most effective against personnel (it tends to produce a few large pieces which are pushed out in the direction of flight, therefore normally down into the ground). In addition at short range, where the trajectory is still pretty flat, HESH can skip off the ground rather than strike it at a sufficient angle to squash and so detonate. Both of these problems could be rectified by adding an additional fusing mechanism and adjusting the casing of the existing HESH round.

    At greater ranges, it is useful to note that while HESH is an adjusted nature, often not achieving a strike on an AFV sized target at 3+ km, even after the three round HESH correction routine. By comparison, 120mm HEAT (as fired by Leo 2, etc.) is an uncorrected round, which I am told will reliably achieve a first round hit at long range. Such are the differences between spin stabilised rounds and modern fin stabilised ones. I suggest that the advances in aerodynamic (fin stabilised) technology have been such that spin stabilised rounds have been outclassed.

    In my view (and that expressed in the piece I refer to), the COE demands a greater variety of ammunition natures. In particular, I would like to see the introduction of HEAT (to directly replace HESH, due to improved accuracy and armour penetration), Cannister, HE (effectively a scaled down 155mm HE, with a front mounted proximity/contact fuse and a case that produces plenty of small splinter) and finally a double impact anti-structure munition (120mm delivered round similar to LASM). All of these rounds could be designed to be fired from the existing rifled 120mm gun, some (esp HEAT) with the use of slipping driving bands; however the R&D and manufacturing costs would be excesive, especially considering that all of these rounds are available already, albeit for the 120mm smoothbore. In the more distant future, it may also be beneficial to ble able to fire missiles from our tank barrels.

    So, to my mind, the question is: "Should we spend money developing and buying UK bespoke ammunition or should we spend money re-gunning CR2 to smooth bore (or perhaps re-turretting is more appropriate) and buying what we want/need more cheaply, quickly, etc?" Unfortunately there is no money so, like so many other things, we'll have to suck it up and work with what we have for the moment.

    I had heard that we weren't in the business of building any more CR2 barrels or HESH and that the supply of both was very much finite. This being the case, someone will have to make a decision at some stage.

    Assuming that rail-gun and laser technology don't suddenly mature in the next few years and there is no reason to up-gun to 140mm or further, I think it is safe to say that we'll move to 120mm smooth-bore at some stage, it is just a case of when and how. The how brings us to the re-gun CR2 or buy Leo2 or even something else? Given that the cost of buying Leo2A6 is about the same as re-turretting CR2, this is not as simple a question as it might otherwise be. clearly if FRES MA/DF (or son of FRES MA/DF) ever comes back on line with a 120mm main armament, this may also have a bearing on the decision .
  14. You'd like this:


    The M-337 120mm HE-MP round the Israelis were developing. I think the M908 MPAT-OR round also does the LASM job you describe.

    Basically it comes down to the fact that most of these rounds are already out there - we just can't use any of them.
  15. I have no doubts it can be done, even at sensible cost. Certainly cheaper than re-turreting CCR2 or replacing it with Leopard 2.