Tanks guns and ammunition.

[Wiedzmin]

@SH_MM

 

 

which 105mm APFSDS is this ?

 

 

[SH_MM]

As far as I know this is Rheinmetall's 105 mm APFSDS design which was not adopted. The same might be true for the improved 105 mm HEAT-FS ammunition mentioned in the same brochure. A lot of other stuff advertised by Rheinmetall (Rheintech) to the US Army was experimental.

[Wiedzmin]

6 hours ago, SH_MM said:

As far as I know this is Rheinmetall's 105 mm APFSDS design which was not adopted. The same might be true for the improved 105 mm HEAT-FS ammunition mentioned in the same brochure. A lot of other stuff advertised by Rheinmetall (Rheintech) to the US Army was experimental.

from bocn

[SH_MM]

 

I wasn't aware that the KE-T round actually had a longer penetrator and higher muzzle velocity than the M829 APFSDS.

[Zach9889]

Wouldn't surprise me if it was a licensed DM33. 

[SH_MM]

This is not a DM33 - length, weight, shape and muzzle velocity do not match.

[Clan_Ghost_Bear]

https://www.gd-ots.com/munitions/large-caliber-ammunition/120mm-kew-a4/

"Along with Rheinmetall"

 

[alanch90]

10 minutes ago, Clan_Ghost_Bear said:

https://www.gd-ots.com/munitions/large-caliber-ammunition/120mm-kew-a4/

"Along with Rheinmetall"

 

99 percent sure its a rebranded DM-63

[SH_MM]

2 hours ago, Clan_Ghost_Bear said:

https://www.gd-ots.com/munitions/large-caliber-ammunition/120mm-kew-a4/

"Along with Rheinmetall"

 

 

Great find.

 

1 hour ago, alanch90 said:

99 percent sure its a rebranded DM-63

 

Yes, the photo in the borchure seems to be a photoshopped DM63. I guess Defence Munition International's spirit lives on.

 

Even the nametags are simple paper glued to the sabot... (enlarge image to see the color difference).

 

[Wiedzmin]

 

 

 

[Alzoc]

Nexter's Ascalon concept undergoing live fire trials at Alcochete (Portugal) :

 

Sadly, no public images available yet.

Ascalon is a 140 mm gun using telescoped ammunition (meaning potentially longer APFSDS rods and more ammunitions onboard) and is the main competitor of Rheinmetal's 130 mm for the MGCS.

 

The energy at the muzzle, is not overly impressive at 10MJ (with a goal of 13MJ by 2025) compared to the 9-12MJ of current 120mm but Nexter claim to reach those energy at a lower chamber pressure than current guns.

 

So we have two concepts going in opposite directions. Rheinmetal's 130mm will have a much higher muzzle energy than the current generation of guns (50% more according to Rheinmetal) which mean that the platform using it will have to be sturdy enough to withstand the recoil, while Nexter is going toward a lower energy gun (compensated by longer kinetic penetrators) which could theoretically be mounted on lighter platforms. That might show opposite visions for the MGCS which lines up somewhat with the operational culture of both country. A heavier tank geared more toward territorial defense for Germany, and a lighter more deployable platform for France.

 

The 130 mm is also using mature and proven technological solutions, while a 140 mm CTA is (as far as I know) something new which may lead to hurdles during the development process. So the maturity of the technology (which will be somewhat linked to the cost) will also be a factor.

[SH_MM]

52 minutes ago, Alzoc said:

while Nexter is going toward a lower energy gun (compensated by longer kinetic penetrators)

 

One cannot compensate lower muzzle energy with a longer penetrator, as the penetrator mass directly affects the muzzle energy.

[Alzoc]

20 minutes ago, SH_MM said:

One cannot compensate lower muzzle energy with a longer penetrator, as the penetrator mass directly affects the muzzle energy.

 

No but a higher velocity will mean a lot more energy loss by friction (be it in the tube or in the air during travel). Mass will stay the same during the whole flight while velocity will decrease quickly.

 

Depending on the distance to the target, a slower heavier round can actually deliver more energy than a smaller faster one. There must be a set distance beyond which the 140 mm will outperform the 130 mm. Depending on the mass and velocity of both rounds it could be completely/mostly useless (like the 140 mm only becoming more interesting  past 4 km) or a fair trade-off (cut-off range around 1 to 2 km). It is somewhat the same idea than 5,56 vs 7,62 mm for rifles past a certain range (assuming you can see the target).

 

Beyond kinetics penetrators, there is also the payload to consider. A programmable 140 mm HE will pack more punch than a 130 mm one, especially if the 140 is fired at lower velocities.

[SH_MM]

38 minutes ago, Alzoc said:

Depending on the distance to the target, a slower heavier round can actually deliver more energy than a smaller faster one. There must be a set distance beyond which the 140 mm will outperform the 130 mm.

 

No, this isn't as simple. The muzzle energy is 1/2 * projectile mass * muzzle velocity. If a projectile/catridge design already has a lower total muzzle energy, then it would have a lower muzzle velocity for a constant penetrator mass. Increasing the penetrator length (and thus the mass) will then result in an even lower muzzle velocity when keeping the muzzle energy constant.

 

The issue is that it is not possible to simply reduce penetrator diameter without potential drawbacks (making the easier to defeat by reactive armor or having issues with bending of penetrator during flight). Obviously air friction will be different for different projectiles moving at different speeds, but the biggest factor for drag/friction are the fins. A faster moving, shorter longrod projectile might require less obstrusive fins than a slower moving rod. Last but not least the trajectory for a slower, heavier rod will be worse. It will have to be fired with an ever so slightly higher elevation to hit the same target, thus it will travel for a longer period of time, being affected by air resistance longer.

 

There is a reason why most APFSDS designs tend to aim to improve velocity and projectile length at the same time, rather than adopting a long, slow spear-like projectile.

 

Obviously there are a lot more factors regarding any final decision between Nexter's and Rheinmetall's guns. Is 13 MJ the muzzle energy of the total projectile (incl. sabot) or is it the weight of the in-flight projectile only? Is the 130 mm APFSDS projectile developed by Rheinmetall actually shorter than the 140 mm version of ASCALON or not?

 

[Alzoc]

52 minutes ago, SH_MM said:

1/2 * projectile mass * muzzle velocity

52 minutes ago, SH_MM said:

obviously air friction will be different for different projectiles moving at different speeds, but the biggest factor for drag/friction are the fins. A faster moving, shorter longrod projectile might require less obstrusive fins than a slower moving rod.

No, both kinetic energy and friction forces are calculated using the squared velocity. So while it is much easier to increase the kinetic energy by increasing velocity, it also mean that for the same initial energy a faster projectile will bleed energy much much faster than a massive one :

 

Spoiler

From wiki :

 

Drag depends on the properties of the fluid and on the size, shape, and speed of the object. One way to express this is by means of the drag equation:

 

 

where

 

is the drag force,

is the density of the fluid,^[17]

is the speed of the object relative to the fluid,

is the cross sectional area, and

is the drag coefficient – a dimensionless number.

 

True the drag coefficient and the surface of the projectile play a part when calculating friction forces. While both will tend to be bigger for a bigger projectile they aren't the most important parameter. The main parameter for energy loss due to friction will always be the relative speed between the projectile and the fluid (air) :

 

Spoiler

The drag coefficient depends on the shape of the object and on the Reynolds number

 

,

where

is some characteristic diameter or linear dimension. Actually it is the equivalent diameter of the object. For a sphere is the D of the sphere itself.

 

For a rectangular shape cross-section in the motion direction, , where a and b are the rectangle edges.

 

is the kinematic viscosity of the fluid (equal to the dynamic viscosity divided by the density ).

 

At low , is asymptotically proportional to , which means that the drag is linearly proportional to the speed, i.e. the drag force on a small sphere moving through a viscous fluid is given by the Stokes Law:

 

 

At high , is more or less constant and drag will vary as the square of the speed. The graph to the right shows how varies with for the case of a sphere. Since the power needed to overcome the drag force is the product of the force times speed, the power needed to overcome drag will vary as the square of the speed at low Reynolds numbers and as the cube of the speed at high numbers.

 

Note the section in bold, at high Reynolds (high velocity) the energy loss due to drag will even depends on the cube of the velocity.

 

For a given initial energy there is always a distance where a heavier projectile will retain more energy than a faster one (unless you are in a vacuum and drag doesn't exist). The higher the velocity of the projectiles, the faster it is to reach that point. But we don't have enough info on the projectiles as of yet to tell at which distance the 140 mm will outperform the 130 mm (and whether or not the projectiles will ever reach said distance). As you said :

 

52 minutes ago, SH_MM said:

Obviously there are a lot more factors regarding any final decision between Nexter's and Rheinmetall's guns. Is 13 MJ the muzzle energy of the total projectile (incl. sabot) or is it the weight of the in-flight projectile only? Is the 130 mm APFSDS projectile developed by Rheinmetall actually shorter than the 140 mm version of ASCALON or not?

 

 

[SH_MM]

1 hour ago, Alzoc said:

No, both kinetic energy and friction forces are calculated using the squared velocity.

 

Sorry, I originally wrote "... mass * v²", then deleted it and wrote "muzzle velocity" as I was talking about the muzzle velocity specifically. I must have accidentally deleted the "²" as well.

 

Yes, obviously the reduction in kinetic energy while be greater when a 5 kilogram projectile moving at 2,000 m/s is reduced by 50 m/s than for a 10 kilogram projectile having its velocity reduced from 1,650 to 1,600 m/s... but there is no indication that the difference will be as pronounced and as relevant.

 

I.e. let me give you an example for which I have data. According to the Swiss firing tables, the Pfeil Pat 87 Lsp (Cart flèche 87 lum) aka the DM23 APFSDS has an in-flight weight of 4.6 kilograms and a muzzle velocity of 1,640 m/s. At 2,000 metres distance, a velocity of 1,529 m/s is reached.  The M829A1 in-flight projectile has a weight of 4.88 kilograms and a muzzle velocity of 1,575 m/s. After travelling 2,000 metres, the velocity is only 1,440 m/s.

 

So in this specific case, the total energy loss is greater for the heavier, slower projectile. Why? Because of the higher drag and higher weight of the M829A1 APFSDS. Only after a longer distance, the DM23 will loose more kinetic energy than the M829A1. How big is the weight/velocity difference between ASCALON and Rheinmetall's 130 mm APFSDS (if there is any)? When the heavier projectile ends up being better after 4-8 kilometers, then it is irrelevant.

 

Regarding your original statement, I can only assume that it is speculation. Apparently Nexter's ASCALON concept as originally announced in April 2021, had a total catridge size of at most 130 cm. Rheinmetall has not revealed the dimensions of its projectile yet, but it seems to be more than 130 cm. So the ASCALON's ammunition - if Nexter did not change the dimensions - is smaller and would rely on Rheinmetall using a smaller projectile/penetrator than physically possible despite potentially having a larger propellant charge in their catridge.

 

The Nexter article also mentions that the ASCALON round will start with a muzzle energy of 10 MJ, suggesting that this is either the in-flight projectile or the penetrator. For the sake of comparison, the OFL F1 should have some 6.3 MJ (penetrator only) and the German DM53 fired from the L/55 should have slightly more than 7 MJ muzzle energy (penetrator only). So ASCALON would be a significant step-up in terms of lethality, but the new KE2020 Neo (in development for the L/55A1) with 20% more muzzle energy and a new composite sabot than DM53/DM63 could come rather close. The 13 MJ are projected growth potential.

[Alzoc]

24 minutes ago, SH_MM said:

How big is the weight/velocity difference between ASCALON and Rheinmetall's 130 mm APFSDS (if there is any)? When the heavier projectile ends up being better after 4-8 kilometers, then it is irrelevant.

 

Agreed, that is the core of the issue.

As we both said we don't have the infos on the mass/velocity of both projectiles yet (though we can indeed speculate based on existing ammunitions). So we don't know if the distance where the energy of both round are equal will represent an interesting trade-off (around 2km) or if it will be completely irrelevant as you said (>4km).

 

24 minutes ago, SH_MM said:

So ASCALON would be a significant step-up in terms of lethality, but the new KE2020 Neo (in development for the L/55A1) with 20% more muzzle energy and a new composite sabot than DM53/DM63 could come rather close. The 13 MJ are projected growth potential.

 

Yes I think that it surprised everyone when they announced an energy of "only" 10MJ at the beginning since it isn't much more (or even less in some cases) than modern 120 mm. The question whether the rod will be heavy enough to have a comparative advantage at some range against those fired from 120 and 130 mm guns is up in the air. Though lower chamber pressure will tend to increase the barrel life and/or lighten the gun (less thickness necessary) which is a nice plus.

[Collimatrix]

On 5/21/2022 at 5:01 AM, SH_MM said:

A faster moving, shorter longrod projectile might require less obstrusive fins than a slower moving rod. Last but not least the trajectory for a slower, heavier rod will be worse. It will have to be fired with an ever so slightly higher elevation to hit the same target, thus it will travel for a longer period of time, being affected by air resistance longer.

 

No.  The stabilizing lift force provided by the fins is a function of angle of attack times fin area times airspeed squared.  The overturning moment acting on the rod is a function of the moment arm between the aero center and center of gravity times airspeed squared.  The stabilizing moment provided by the fins is a function of their stabilizing lift force times the moment arm between the fins and the center of gravity.  Thus, as long rods have gotten longer and longer, these competing effects have more or less canceled out and the fins have stayed about the same size.

 

Because the stabilizing force provided by the fins is a function of airspeed squared and the overturning force is also a function of airspeed squared, a long rod penetrator that's stable at one airspeed is stable at any airspeed.  The only exception is the transonic where lift coefficients and aero centers can jump around, but that's pretty much academic because an APFSDS long rod going transonic velocities isn't going to be killing very much.
 

[Collimatrix]

Ascalon seems terrible, WTF are they thinking?

[Alzoc]

2 hours ago, Collimatrix said:

Ascalon seems terrible, WTF are they thinking?

 

As far as I see it they are aiming for a moderate to no increase in penetration (keeping in mind the effective range of heavier vs faster rod discussion) while having an overall lighter and more compact turret+gun combo compared to the current generation. Thus the question of why do it for a 140 mm gun instead of keeping a 120 mm (same principles should apply)?

That or I'm missing something or we are missing a piece of the info.

[FORMATOSE]

On 5/13/2022 at 12:33 PM, SH_MM said:

As far as I know this is Rheinmetall's 105 mm APFSDS design which was not adopted. The same might be true for the improved 105 mm HEAT-FS ammunition mentioned in the same brochure. A lot of other stuff advertised by Rheinmetall (Rheintech) to the US Army was experimental.

 

 

5 hours ago, Collimatrix said:

Ascalon seems terrible, WTF are they thinking?

 

Nexter is offering a 140 mm gun which is, obviously, more powerful than the current 120 mm ones while not having the drawbacks of the envisioned 130-140 mm tank guns, such as the recoil forces (thanks to its muzzle brake) and bulky ammunition (140 mm cased telescoped ammo will have a length equal to or less than 130 cm).

Those two characteristics allow ASCALON to be integrated on tracked vehicles weighing less than 50 t, thus more potential customers.

[Collimatrix]

20 hours ago, Alzoc said:

 

As far as I see it they are aiming for a moderate to no increase in penetration (keeping in mind the effective range of heavier vs faster rod discussion) while having an overall lighter and more compact turret+gun combo compared to the current generation. Thus the question of why do it for a 140 mm gun instead of keeping a 120 mm (same principles should apply)?

That or I'm missing something or we are missing a piece of the info.

Their overall design rationale reminds me a lot of the conceptual studies in British tank guns that led up to the 120mm L11.  Lower breech pressure means that the breech, ceteris paribus can be narrower and thus take up less room in the turret because the breech ring and barrel don't need to be as thick.  This also makes stabilization a little easier because there's less steel for the stabilizer to have to wrestle with.  Lower peak pressure also makes life a little easier for the ammunition designers because the interface between the sabot and the dart is experiencing less peak force.

The problem with this line of thinking is that it's really hard to get the raw performance.  Kinetic energy of the projectile is the integral of the pressure at the base of the projectile swept along the volume of the bore.  For a given mass of propellant, higher pressure guns have better thermodynamic utilization of the propellant.  In small arms, higher peak pressure also gives more consistent internal ballistics and thus accuracy, but I am not sure if this is a major factor in tank guns.

The Rheinmetall 130mm has the same cartridge base dimensions as the 120mm:



So the increase in breech thrust against the breech block and the stress in the firing chamber and breech ring should only be greater by (approximately) the percentage increase in pressure.  On top of that, the breech designs Rheinmetall has shown have a more sophisticated wedge design that existing 120mm guns which should provide better distribution of the firing loads and thus lower peak stress:



There may also have been metallurgical improvements in gun breech materials in the... what, half century since the 120mm smoothbore was invented?

So the width increase of the 130mm vs. the 120mm may be very small.  The gun will probably need greater recoil travel and may need to be mounted further back in the turret, so it is not space-neutral or anything like that.  However, with the current manned tank turret design of placing the gunner, gun, and commander abreast (or loader, gun and gunner in designs with a flesh loader), the width of the gun breech is dividing the turret right down the center and determines to a large degree how much elbow room is left for the crew for a given turret ring diameter.

So, given that the Rheinmetall design is more mature, more powerful, and shouldn't be too much wider than the existing 120mm smoothbore, the advantages the Ascalon offers seem poor by comparison.

[Lord_James]

8 hours ago, Collimatrix said:

On top of that, the breech designs Rheinmetall has shown have a more sophisticated wedge design that existing 120mm guns which should provide better distribution of the firing loads and thus lower peak stress:


 

What about this breach is more sophisticated compared to the L/44 or L/55’s breach? Wouldn’t the recoil system be the peice that reduces the peak stress on the vehicle mounting the weapon, and wouldn’t the propellant design and chemistry determine its peak pressure within the tube? 

[Collimatrix]

12 hours ago, Lord_James said:

What about this breach is more sophisticated compared to the L/44 or L/55’s breach? Wouldn’t the recoil system be the peice that reduces the peak stress on the vehicle mounting the weapon, and wouldn’t the propellant design and chemistry determine its peak pressure within the tube? 

The interface between the sliding wedge of the breech block and the breech ring is what is improved.



As you can see, on the M256 the shoulder in the breech ring that the sliding wedge rests against is a single element that's more or less a square corner (albeit radiused).  In the Rheinmetall 130mm weapon you can see that the interface between the sliding wedge and the breech ring has two layers, and that it's sort of a rolling teardrop shape with a much more generous radius.  It's not unlike what the US was looking at with the XM360:



It's been known for a very long time that this sort of design of sliding wedge is stronger, but it's traditionally been considered too much of a pain in the ass to manufacture to be worth it.  Perhaps computer stress modelling and improved manufacturing technology have changed that.

By reducing stress I mean it reduces stress in the metal of the breech mechanism.  The stress at any given point in the breech ring and the breech block has to be lower than the yield strength of whatever uber-steel it's made out of so the gun isn't permanently deforming itself with each shot.  Ideally the stress should be quite a bit lower in order that the mechanism has good fatigue life.  When the original 120mm Smoothbore was designed (late 70s) I doubt that full computational finite element analysis was possible; the computers were too pathetically weak back then.  The stress analysis was probably done with some computer modelling, but also good old fashioned rules of thumb and photoelastic stress simulations:



It is possible to modulate pressure within the tube with propellant design, but to what end?  Yes, pressure in the breech is what causes the stress on the locking elements.  Pressure in the breech is also what makes the projectile go downrange.

Keeping the peak recoil force within reasonable bounds is important as well, so I suspect that the recoil system on the 130mm will need to permit the gun to travel further than the system in current 120mm armed vehicles.  However, increasing the travel of the gun during recoil doesn't really change the width of the gun system that much.  Look at how cramped the gunner's position is in an Abrams, which is supposed to be one of the MBTs with more generous elbow room:



That position, by all accounts, kind of sucks, but if the gun gets even a few centimeters wider it's going to suck way more.

[Sturgeon]

18 hours ago, Collimatrix said:

Perhaps computer stress modelling and improved manufacturing technology have changed that.

 

I can guarantee this is a factor.