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PostPosted: Mon Dec 26, 2016 1:17 am 
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In classical ordnance terminology a Mortar fires only above 45 degrees, a Howitzer can fire below 45 degrees. Of course this gets messed up by these modern 'mortars' that fire at low angles, but that's why language evolves. So taking the mortar's secondary characteristics, we might say its a low pressure, low velocity weapon that's typically smooth bored and fin stabilised. :)

Michael, I'm not doubting you. But I have to admit that muzzle loading surprises me, and I'm struggling to see the rationale behind it compared to AMOS. under the circumstances I'm arguing against it, or suggesting its wrong, I'd just love to know why. The only one that leaps to mind is gas control, AMOS had rather generous bore evacuators, however it'll all come out sooner or later :D

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PostPosted: Mon Dec 26, 2016 9:00 am 
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Well so far the suggestions I've seen is that it allows for higher rate of fire, is more reliable with less components compared to AMOS, weighs less, allows for usage of STRIX (it appears uncertain if they can be made to fit in the AMOS autoloader) and is part of the resason that the considerably cheaper.
The cost for 40 units minus the CV90 hulls are 575 million SEK for Mjölner, apparently AMOS would have cost 1.5 billion SEK so quite the difference.

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PostPosted: Mon Dec 26, 2016 7:23 pm 
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I saw that, but 'less complicated' and a 'higher rate of fire' are where I start asking questions.

Just thinking it through. The projectile has to come out of its storage position and be bought up to and into alignment with the tube, and for a first assumption lets say that's the same time for both ML and BL. From that position the BL gun has to ram the projectile into the breech, that's its own length, plus the depth of the breech, plus clearances lets call that 1m max (and more like half that). To Muzzle load the projectile has to move the most of the length of the barrel (about 3m), plus it own length, there are a lot of other factors I can't even guess at that may add or equally subtract distance. But the barrel outside the turret and its own length are pretty certain and I'm going to call that 2m as an approximation.

So on this utterly crude base line, the ML projectile has to move twice the distance (plus the drop time) if compared to the BL system. This suggests either the ML projectile is moving faster per loading cycle, or there is a chain of projectiles that each only have to move a much shorter increment. If developments have allowed the projectile to be moved faster this would apply equally to both. If there is a chain of projectiles then I would certainly accept a higher rate of fire, but less complication?

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PostPosted: Mon Dec 26, 2016 7:45 pm 
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I think the less complicated bit may refer to it being less complicated to use in conjunction with a human loader element. From the looks of it the human just have to stuff the fairly high up rails, with a breech loader you'll be further down and mucking about.

I don't have much more details to help with the arisen questions but AMOS can burst fire at 16 rounds per minute, sustained at 12. The Mjölner prototype can apparently do 18 rounds per minute sustained.

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PostPosted: Mon Dec 26, 2016 8:21 pm 
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KDahm wrote:
My understanding of the difference between mortar and small howitzer is in the propellant location and muzzle velocity.

The mortar has a loose or soft propellant that is attached to the base of the actual shell. Also, the velocity is sub-sonic and the shells generally need fins for stability.

A howitzer has a propellant charge in a brass, zinc, or steel case that is loaded with the shell or separately, or in silk bags for the really big guns. The case is left behind on firing, and the velocity is Mach 2 or better.

Breechloading or not doesn't matter to a mortar description. It's just easier on the smaller mortars to drop it down the muzzle. For a vehicle mounted mortar, I can see a breechloading type, with two chambers, one under the barrel and the other being loaded with a new shell. After firing, the chambers are rotated to exchange places.


Nope. The definition of mortars and howitzers is far, far older than that. Howitzers and mortars existed long before propellant charges in brass, zinc or steel cases were invented.


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PostPosted: Mon Dec 26, 2016 9:55 pm 
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David Newton wrote:
Nope. The definition of mortars and howitzers is far, far older than that. Howitzers and mortars existed long before propellant charges in brass, zinc or steel cases were invented.

Yes, but we were talking about modern usage, post-1890. Otherwise, it would get into discussions about torpedoes vs mines, and other such minutae.

There's also the lively discussion from Mid-December about cruisers, destroyers, and frigates.

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PostPosted: Tue Dec 27, 2016 10:39 am 
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KDahm wrote:
David Newton wrote:
Nope. The definition of mortars and howitzers is far, far older than that. Howitzers and mortars existed long before propellant charges in brass, zinc or steel cases were invented.

Yes, but we were talking about modern usage, post-1890. Otherwise, it would get into discussions about torpedoes vs mines, and other such minutae.

There's also the lively discussion from Mid-December about cruisers, destroyers, and frigates.


Even in modern usage its intended function that drives form and determines description.
Prime Function
Direct Fire - shoots directly at targets as close to line of sight as physics allow, think rifle. These are Guns or Canon.
Indirect Fire - shoots indirectly at targets, lobbing the projectiles at targets that typically can not or are not directly visible from the weapon. These are Howitzers and Mortars

Secondry Function
Upper Register - Above 45 degrees
Lower Register - Below 45 degrees

Indirect Fire weapons optimised to fire in the Upper Register are Mortars
Indirect Fire weapons optimised to fire in the lower register are Howitzers

These are intended uses, a mortar can be used for DF, it generally sucks at it, as its not optimised for the job and the compromises involved rob it of DF potential. A Howitzer is a lot better at DF but still not as good as a canon. A cannon can do indirect fire perfectly well too, but again its not optimised for role, it's typically higher MV compromises its efficiency in the task, low throw weight and payload for high expenditure of propellant, rapid barrel wear and poor fragmentation - but as an AA weapon its still perfectly happy shooting at 90 degrees, so elevation is a secondary factor.

Now in 'sucking at DF' a 120mm mortar might still be a perfectly useful weapon, indeed better than 120mm canon for somethings - like flinging the maximum HE load at a slow moving (better yet stationary) target at close range. But that's a niche function and much of anything that improved the DF capability of that mortar will come at the expense of its primary IDF capability. Likewise adapting a 120mm tank canon into an artillery piece is unlikely to help its DF tank busting capability. Its all about the compromises inherent in the function that generate the form. Firing in the upper register gets you the most range for your bang, so velocity can be traded off for throw weight and payload, with a lighter lower pressure barrel burning less propellant. DF is the exact opposite, its the least efficient in terms of range for velocity, so barrel, projectile and propellant have to be traded for MV even if you're not worried about punching holes in something down range. its late and I'm waffeling sorry

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PostPosted: Tue Dec 27, 2016 11:21 am 
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The Argus wrote:
Even in modern usage its intended function that drives form and determines description.
Prime Function
Direct Fire - shoots directly at targets as close to line of sight as physics allow, think rifle. These are Guns or Canon.
Indirect Fire - shoots indirectly at targets, lobbing the projectiles at targets that typically can not or are not directly visible from the weapon. These are Howitzers and Mortars

Secondry Function
Upper Register - Above 45 degrees
Lower Register - Below 45 degrees

Indirect Fire weapons optimised to fire in the Upper Register are Mortars
Indirect Fire weapons optimised to fire in the lower register are Howitzers

{SNIP}

shane

A quick survey of modern (post 1970) 155mm artillery pieces indicates that the maximum elevation for most of them lies in the 70 to 75 degree range. This is of course useful for Time on Target barrages at less than maximum range, but would put them into Mortar category by the classic definition. This is backed up with videos indicating that the preferred method for shorter range shoots is to increase the elevation and have the shot fall more vertically onto the target, rather than having lower than 40 degree elevations.***

Therefore, we need a functional definition to distinguish between the two in modern usage. I would submit that my above shorthand is a decent starting point.

Justice Potter Stewart wrote:
I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that.


***I am not an artilleryman, nor have I more than skimmed the applicable US Army TMs. Please correct if I am wrong.

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PostPosted: Tue Dec 27, 2016 11:37 am 
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I'm baffled as to why the tracked muzzle-loader still lives. ( Honourable exception of IDF, of course, of course !!) Surely the external mechanics are vulnerable to 'small arms' ie 10~20mm damage...

Going back to gun-forts, there were 'pop-up' muzzle loaders that had an 'outside turret ring' rammer and a sprung-loaded, double-jointed elevator / recoil system so loaded level, then lift above parapet, and recoil recovered the weapon to 'load' position...

But, their rammer was entirely inside the fort's protection...

Even in the confined space of a modern AFV turret, you'd think there'd be room for a basic 'revolver' system so you're loading the spare slots while the business pair are breech-loading the mortar tubes...

Oh, and a modest supply of compressed air to blow the residue out ??

Very strange.

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PostPosted: Tue Dec 27, 2016 10:57 pm 
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KDahm wrote:
A quick survey of modern (post 1970) 155mm artillery pieces indicates that the maximum elevation for most of them lies in the 70 to 75 degree range. This is of course useful for Time on Target barrages at less than maximum range, but would put them into Mortar category by the classic definition. This is backed up with videos indicating that the preferred method for shorter range shoots is to increase the elevation and have the shot fall more vertically onto the target, rather than having lower than 40 degree elevations.***

Therefore, we need a functional definition to distinguish between the two in modern usage. I would submit that my above shorthand is a decent starting point.

Justice Potter Stewart wrote:
I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that.


***I am not an artilleryman, nor have I more than skimmed the applicable US Army TMs. Please correct if I am wrong.


As I said before mate there's a lot of overlap particularly with howitzers - it's what they are for, that flexibility is the point of them. Admittedly the whole 45 business is a bit nominal these days, a rough guide line. It had more weight in ye olden days, when 45 degrees was taken to be 'max range' with any given charge, So perhaps 'BO' (ballistic optimum) might be a better term for the dividing line between upper and lower registers. That is to say the BO is such elevation as gives the maximum ballistic range the weapon is capable of with a given projectile and charge. These days the ballistic optimum for modern field howitzers going for distance more like 50 to 55 degrees (IIRC), as we've come to exploit the drag reduction to be had getting the shell up into thinner air sooner.

Besides adjusting its fire, a Howitzer may want to fire above its BO for a number of reasons, ToT is one, there's also crest clearance and several others. But these are extra capabilities, like the added tools on a Swiss Army Knife - at the end of the day it's still a knife. A howitzer would still be a howitzer even if it couldn't fire at more than 45 degrees, just as it doesn't become a gun if firing over open sights.

But if you don't like elevation, then velocity or breech pressure are a better fit than any compound of derivative factors, as at least they are primary design elements dictated by the function. Mortar = low, Howitzer = medium, and Gun/Canon = high...

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PostPosted: Wed Dec 28, 2016 10:29 am 
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Nik_SpeakerToCats wrote:
Even in the confined space of a modern AFV turret, you'd think there'd be room for a basic 'revolver' system so you're loading the spare slots while the business pair are breech-loading the mortar tubes...

Oh, and a modest supply of compressed air to blow the residue out ??


They probably already have an air compressor on board. The engine load would be small.

I have concerns with a revolver design. Obturating the cylinder gap would be difficult without going to something like a Nagant Gas Seal type design, and that employs a cartridge case.

As far as nomenclature is concerned, most howitzers today have a long barrel, and are often referred to as gun-howitzers, as they display the characteristics of both. They can fire flat or they can fire high.

Most mortars cannot fire flat. Those that do, are mainly called mortars because they fire the same kind of ammunition (or close to it) as a traditional Stokes-Brandt mortar.

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PostPosted: Wed Dec 28, 2016 11:33 am 
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Hey, the data needed is the first one in the google search for "Mortar Chamber Pressure": http://www.dtic.mil/dtic/tr/fulltext/u2/a503149.pdf

Anyway, the peak pressures, depending on the mortar, appear to be in the range of 10,000-15,000 psi. That's in the range of shotgun pressures. SAAMI spec for a 357 magnum is 35,000 psi. That can easily be handled by either a close wiper fit between the two-chamber revolver, or by having a 1/8" or 1/4" lip where the revolver is raised after rotating into position.

Incidentally, the 155mm howitzers appear to have chamber pressures in the 55,000 to 60,000 psi range.

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PostPosted: Wed Dec 28, 2016 11:39 am 
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"I have concerns with a revolver design. "

A revolver *loader,* so you top-load one set of slots while the other is being rammed into breech which is then sealed in usual way...

Long ago and far away, I've a vague memory of a 'three-gun' loader (**) which could turn clockwise or anti-clockwise to present a choice of 'ready' devices. This would be a 'six-gun', albeit two at a time...

**) It may have been a pipe-line 'pigger'...

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PostPosted: Wed Dec 28, 2016 11:42 am 
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The Russians have a clip-loaded breech-loading 82mm mortar, the 2B9M Vasilik. It was supposed to be very effective in Afghanistan. (I underline the supposed because the fanboys have poisoned the pool pretty thoroughly on the effectiveness of Russian and Chinese kit)

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PostPosted: Wed Dec 28, 2016 12:18 pm 
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Nik_SpeakerToCats wrote:
"I have concerns with a revolver design. "

A revolver *loader,* so you top-load one set of slots while the other is being rammed into breech which is then sealed in usual way...

Long ago and far away, I've a vague memory of a 'three-gun' loader (**) which could turn clockwise or anti-clockwise to present a choice of 'ready' devices. This would be a 'six-gun', albeit two at a time...

**) It may have been a pipe-line 'pigger'...

I was thinking of an actual two chamber revolver. One chamber is rotated into position under the barrel, then the other is top-loaded and waiting. The design could be made similar to a ADEN cannon or Mauser BK 27, but simplified because of the much lower pressures and rate of fire. Because of only having two chambers, the rotating section would be a bar rather than a round section. O-O

I can almost see the mechanism in my head.

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PostPosted: Wed Dec 28, 2016 12:20 pm 
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Francis Urquhart wrote:
The Russians have a clip-loaded breech-loading 82mm mortar, the 2B9M Vasilik. It was supposed to be very effective in Afghanistan. (I underline the supposed because the fanboys have poisoned the pool pretty thoroughly on the effectiveness of Russian and Chinese kit)



Image

The underlying Wikipedia article doesn't give a clue as to how the clip loading feature works.

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PostPosted: Wed Dec 28, 2016 3:58 pm 
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Nik_SpeakerToCats wrote:
I'm baffled as to why the tracked muzzle-loader still lives. ( Honourable exception of IDF, of course, of course !!) Surely the external mechanics are vulnerable to 'small arms' ie 10~20mm damage...

Commonality of ammunition?

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PostPosted: Wed Feb 08, 2017 10:49 am 
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An update now. A test rig has been assembled using the prototype mortar equipment and a CV90 chassis and it was test fired on February 1st.
The test was to confirm calculated loads and strain on the vehicle when firing, they were all found to be within acceptable limits.
Image

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PostPosted: Tue Oct 10, 2017 1:25 pm 
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And a small update again. The numbers quoted - ROF and such - looks good.
Quote:
Land Platforms
Sweden’s twin 120 mm mortar system takes shape
Christopher F Foss - IHS Jane's International Defence Review
08 October 2017
Key Points

•The Swedish Army’s new Mjolner twin 120 mm mortar system is expected to undergo firing trials
Forty Swedish Army CV90 infantry fighting vehicles will be equipped with the Mjolner system
•BAE Systems Hagglunds is set to conduct manned firing trials of a prototype/demonstrator of the 120 mm Mjolner twin mortar system that it is developing for integration into CV90 infantry fighting vehicle (IFV) in Swedish Army service.

The SEK575 million (USD68 million) fixed price contract was awarded to BAE Systems Hagglunds by the Swedish Defence Material Command (FMV) in December 2016 to provide army mechanised battalions with a highly mobile and survivable indirect fire capability. The vehicles will be designated GRKPBV90.

Under the terms of the contract, the company will supply the first production standard Mjolner 120 mm twin mortar system in 2019, with a total of 40 delivered by 2020.

These will be integrated into CV90 platforms originally built for the 120 mm AMOS (Advanced MOrtar System), which had been jointly developed by BAE Systems Hagglunds and Patria to meet the requirements of Finland and Sweden.

The Mjolner comprises two 120 mm smoothbore mortars that are muzzle loaded using a mechanical ammunition handing system. The system is operated by a four-person crew of the driver, commander, and two ammunition loaders.

According to BAE Systems Hagglunds, the system takes less than two minutes to come into action and carry out a fire mission and with the first four 120 mm mortar bombs being fired in about eight seconds.

It takes less than one minute to come out of action and maximum rate of fire is stated to be up to 16 rounds a minute with a sustained rate of fire of up 10 rounds a minute.

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PostPosted: Thu Jan 11, 2018 10:28 am 
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Some video and footage of final trials of the pre-production rig is now available. Shows a bit more how the system functions.

The loading mechanism is a handpowered one where loaders place mortar rounds into two rails and then operate mechanical levers which moves the rounds forward and out through the hull and into the tubes at the front end.
Video available on this page, some talk in Swedish but interesting when they operate the loading system:
http://www.fmv.se/sv/Nyheter-och-press/ ... sselbiten/
The magazine is reloaded from the outside and placed individually in these small tubes, then grabbed by the loaders from the other end on the inside of the vehicle.
Image
Image
Sort of visible here, but better in the video, is what looks like a protective hood/cover that goes over the firing tubes when not in use.
Image

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