Comparing Jagdtiger 128mm gun vs T72 125mm gun

[Sequoia]

I can understand the newer vehicle has the improved ammunition over what was available in 1945, but would 2 "vanilla" AP rounds (if there is such a thing) from the 2 vehicles have essentially the same penetrating power, and if not, why? I'm looking to be educated.

 

Thanks 

[Vanir Ausf B]

4 hours ago, Sequoia said:

would 2 "vanilla" AP rounds (if there is such a thing) from the 2 vehicles have essentially the same penetrating power?

Not even close. The German 128mm would penetrate about 272mm of RHA at 100 meters. The Russian 125mm firing 1990s-era ammunition would penetrate 600-650mm of RHA at 2000 meters.

For one thing, the penetrators are made of different materials. The 128mm shell is steel while the 125mm sabot is either tungsten or uranium, much denser metals than steel. Also, the penetrators are shaped radically different. The 128mm shell looks like a very large bullet. The 125mm cannon fires a shell containing a submunition called a sabot. The outer layers of the shell peel away in-flight leaving the sabot, which is only about an inch in diameter but nearly two feet long. That means the kinetic energy is concentrated into a very small area. It's the difference between sticking someone with a knife and striking him with your fist. 

Edited August 19, 2017 by Vanir Ausf B

[c3k]

The German gun, the 12.8cm Pak 44, had a muzzle velocity of 950 m/s. The Soviet 125mm smoothbore, depending on round and variant of the gun, fires at about 1700-1800 m/s.

Energy goes up with the square of velocity. Ignoring materials and shaping, the Soviet weapon puts 4 times the energy behind each round. As VaB mentions, that 4x energy, due to shaping and materials, stays with the penetrator over a longer distance (less drag) and is delivered more efficiently (materials and shape) and into a smaller area (shape).

[Sequoia]

I'm hearing you say their are no comparable shells between 1944 and now . I assume the increased velocity is due to superior propellants in the casing?

[Sailor Malan2]

6 hours ago, Vanir Ausf B said:

Not even close. The German 128mm would penetrate about 272mm of RHA at 100 meters. The Russian 125mm firing 1990s-era ammunition would penetrate 600-650mm of RHA at 2000 meters.

For one thing, the penetrators are made of different materials. The 128mm shell is steel while the 125mm sabot is either tungsten or uranium, much denser metals than steel. Also, the penetrators are shaped radically different. The 128mm shell looks like a very large bullet. The 125mm cannon fires a shell containing a submunition called a sabot. The outer layers of the shell peel away in-flight leaving the sabot, which is only about an inch in diameter but nearly two feet long. That means the kinetic energy is concentrated into a very small area. It's the difference between sticking someone with a knife and striking him with your fist. 

The logic is exactly right but I am afraid you have the term Sabot backwards. The Sabot is the light jacket or sheath whose job is to keep the sub-calibre penetrator centred in the barrel whilst being as light as possible. (This means the sabot falls away leaving the tungsten or depleted uranium penetrator to fly on, with less cross sectional area and hence less drag but most of the energy imparted by the propellant, which it applies to a much smaller area of the target than a full calibre round would, as you say).

The APDS designation (and its more modern versions like APFSDS etc) means Armour Piercing Discarding Sabot (i.e. it is the Sabot that is discarded)

[Sailor Malan2]

17 minutes ago, Sequoia said:

I'm hearing you say their are no comparable shells between 1944 and now . I assume the increased velocity is due to superior propellants in the casing?

No and yes. Guns have pretty much always been designed to a maximum chamber pressure, and propellant mass is set to achieve that. There are also secondary effects like barrel wear and peak temperature (which can also be linked to propellant). The more modern guns have better metallurgy and hence allow somewhat higher chamber pressures whilst keeping gun weight sensible, but also more modern propellants allow higher velocities without undue barrel wear, I am not an expert but I presume it is more to do with predictable and consistent burn rate, rate of change of pressure etc rather than pure "power". Anyone want to step in?

[General Jack Ripper]

27 minutes ago, Sequoia said:

I'm hearing you say their are no comparable shells between 1944 and now . I assume the increased velocity is due to superior propellants in the casing?

I think it's more the design of the cannon.
The 12.8cm is adapted from a field gun, I.E. it was not designed specifically for tank fighting.

It's much the same comparison between the U.S. 3-Inch gun, and the 75mm L/70 on the Panther.
One is a gun adapted for use in a tank, the other was specifically designed with tank fighting in mind.

[Sequoia]

Sounds then my choosing the Jagdtiger' s gun as my WWII weapon of comparison was not the best choice but I needed something with a gun diameter comparable to today's tank guns. Let me approach this at a different angle. The 88 on a Tiger 2 had a greater penetration and range than the 88 on a Tiger I as I understand it. Now I know the Tiger 2's barrel was longer but that wasn't the cause of the difference I'm sure. Would this be a case of a different round type perhaps due to superior or more propellant?  

[Sailor Malan2]

No, I think it is just the barrel length which allowed a bigger propellant charge. The peak design chamber pressure is probably the same, and the decay is such that if you use a bigger charge on the Tiger I gun there is still a lot of pressure available at the muzzle (which is wasted and also produces a big flash). The Pak 43 can use this energy, so had a bigger (longer) cartidge with more propellant. The barrel lengths were 56 calibres and 71 (IIRC) so over 10% longer in the case of the Tiger II gun...

I can't find the details of the charge weights.

[Sequoia]

But the longer barrel on the Tiger 2 required a bigger turret, hence a bigger and heavier vehicle right?

[Vanir Ausf B]

6 hours ago, Sailor Malan2 said:

The logic is exactly right but I am afraid you have the term Sabot backwards. )

Good catch. That's what I get for posting at 3AM 

[Vanir Ausf B]

9 hours ago, c3k said:

The German gun, the 12.8cm Pak 44, had a muzzle velocity of 950 m/s. The Soviet 125mm smoothbore, depending on round and variant of the gun, fires at about 1700-1800 m/s.

Energy goes up with the square of velocity. Ignoring materials and shaping, the Soviet weapon puts 4 times the energy behind each round. As VaB mentions, that 4x energy, due to shaping and materials, stays with the penetrator over a longer distance (less drag) and is delivered more efficiently (materials and shape) and into a smaller area (shape).

Right, although I think your projectile weights may be off. Or mine are

There are various muzzle velocities listed for the Pak 44. There were three different powder charges, and apparently AP ammunition both with and without a ballistic cap. WW2 Ballistics lists muzzle velocity for APCBC as 845m/s (lower than the Wiki page which quotes Ian Hogg for the 950m/s figure), which nets about 10 megajoules. At 950m/s it would produce 12.7 MJ.

125mm 3BM42M (a tungsten alloy penetrator) has a MV of 1750m/s and an unconfirmed penetrator weight of 4.6 to 4.85kg, which comes out to about 7 MJ.

 

[Sequoia]

Thanks for mentioning there's a Wiki page if I want more detail on various weapons. I'm not surprised the info is there. Is it found under each vehicle individually or is it summarized together at a particular page?

[Vanir Ausf B]

3 minutes ago, Sequoia said:

Is it found under each vehicle individually or is it summarized together at a particular page?

Individual cannons have their own pages but technology categories have overview pages, such a for APDS and APFSDS

[c3k]

LOL, as Vanir has just mentioned, there are a wide variety of shells and powder charges available to the various weapons. Date of use may change some of those numbers, etc.

It's not as easy as just saying "Gun 1 does this and Gun 2 does that". There are modifiers to each statement: "Gun 1 does this...using ammo x at a range of y, against target z". 

There's a whole specialty devoted to the arcana of this stuff.

[General Jack Ripper]

15 hours ago, Sequoia said:

Thanks for mentioning there's a Wiki page if I want more detail on various weapons. I'm not surprised the info is there. Is it found under each vehicle individually or is it summarized together at a particular page?

As always, take wiki with a small grain of salt. Sometimes the sources being used are not accurate, or simply outdated.

[Michael Emrys]

38 minutes ago, SLIM said:

As always, take wiki with a small grain of salt. Sometimes the sources being used are not accurate, or simply outdated.

And often the information presented is less than complete. But generally it is fairly accurate as far as it goes. So, depending on how far you want to go, you may need to check other sources to get the whole picture. Wiki serves as a good jumping off point for enquiry, but you may need to go that extra mile on your own.

Michael

[JonS]

Several years ago I compared the 76mm gun on the Scorpion to the ... 88mm on the Tiger, I think it was. And also a BMP to the Tiger.

In both cases the Tiger is absolute toast, which was kinda sobering.

Edited August 21, 2017 by JonS

[Sgt.Squarehead]

Thought the 2A20 115mm might give a better comparison, but even that didn't have a true APBC round in the WWII sense, suffice it to say that the 'monkey ammo' for that weapon had higher penetration than the German 128mm and IIRC the Soviets classified 'penetration' to a more rigorous standard than NATO.

Edited August 21, 2017 by Sgt.Squarehead

[Sequoia]

2A20 ?

[Vanir Ausf B]

It's the 115mm cannon mounted on the T-62 tank.

[MikeyD]

I believe the 115mm gun's APFSDS on the T-62 was purpose-designed to pierce the frontal armor of a Centurion from 1,000(?) meters (it may have been from 1,500). They didn't over-design the dart penetrator. If steel could do the job why go expensive with tungsten? It was a better round than NATO 105 mm APDS, light years ahead of the M48's 90mm. As western armor improved and combat ranges increased due to better western guns the Russians upped their game to keep pace. Centurion Mk8 had a 120mm bow angled at 57 degrees, the older Mk3 was only 76mm.

[hank24]

On ‎19‎.‎08‎.‎2017 at 5:23 PM, Sailor Malan2 said:

The more modern guns have better metallurgy and hence allow somewhat higher chamber pressures whilst keeping gun weight sensible

Another fancy measure to increase the possible chamber pressure is 'autofrettage'. Here, an unbelivable high oil pressure ist applied to the inside of the barrel to deform the inner half of it beyond elasticity. So, when the pressure is released, the inner half is compressed by the outer perimeter, it is pre-compressed. On shot, the chamber pressure first has to bring this pre-compression to zero before it can build up a tension.

Don't know wether the Russians are doing this, it is done with the Rheinmetall gun of Leopard2.

First applied on ship guns around 1875 with hot rings drawn over the barrel, cooling down there and compressing it. Saves a lot of top weight.

[JonS]

And not to be confused with autofrottage

[Sgt.Squarehead]