Cobalt is the typical matrix material for tool grade WC. With qualities differing by Cobalt content and sintering pressure.

The numbers for the M993 seem pretty bad. Low grade material. Its an YG 15 (ish) grade. The low end of tool grade WC.

The numbers presented for the SmK(H) are indeed consitent with a WHA but it is extremly unlikely that at this point in time it really has been one. More likely is a WC with Copper-Nickel matrix.
Regardless of if the core of SmK(H) really is a WHA or not what is plain obvious from the two sets of numbers is the difference in actual W contend. The SmK(H) core is 90 W. The M993 core only 76 %. YG 15 WC is better than hardnened steel but as mentioned the poorest (cheapest) WC. It should be rather flexible and shatter resistant for a WC though. I think its pretty obvious that the material properties of the SmK(H) are better for violently punching trough stuff.

The M993 propably is a "victim" of modern engineering.
With the SmK(H) back in the day they tried the impossible and went full overengineering and money doesn't matter. Squeezing every little bit out of performance possible at the time out of it.
The M993 most likely has been designed and optimised to meet a specific specification, achieve this in the cheapest possible way and do nothing more. Obviously they succeeded in this sind everybody seems pretty happy with the result. The M993 and its counterparts in other nations are even happily issued en mass for use in MG belts. I doubt this would be the case with the SmK(H) nowadays.

EmericD said:

I would say that the SMKH is WC embeded in a Nickel - Copper matrix, while the M993 is WC embeded in a Cobalt - Iron matrix.

Are there any commercial examples of a WC - Nickel - Copper alloy? 

Googling, I can find a ton of WC - Cobalt alloys. 

But everything I turned up googling 'Tungsten Carbide Nickel Copper alloy' or 'Tungsten Nickel Copper alloy' all turn up numerous WHA ~90:6:4 alloys, but no mention of a Tungsten Carbide alloy with Nickel and Copper? 

gatnerd said:

Are there any commercial examples of a WC - Nickel - Copper alloy? Googling, I can find a ton of WC - Cobalt alloys.

It's because Nickel or Cobalt are not used to form an alloy with WC, but are used as a binder.

For example :

https://www.vistametalsinc.com/tungsten-carbide-grade-chart/

And a patent from 1977 that describes the use of Ni-Fe matrix with WC, with better mechanical results than Co matrix.

https://patents.google.com/patent/CA1090523A/en

gatnerd said:

Are there any commercial examples of a WC - Nickel - Copper alloy? 

Yes: W90NiCu specified in ASTM B 777-07
This is the alloy consitent with the numbers of the SmK(H). But I really doubt this is really the material.

Because there also is a sintered WC sinter material with the same composition.

The difference is in the way of production. To form a alloy all ingrediences have to be molten and mixed while in liquid state (this is the definition of alloy). Once they are coolded down and solidified the solid mixture is an alloy. This is not possible with all compositions of ingredience and all amounts. The trick is the right mixtures, correct temperatures and cooling speed. Its basically a science in itself.

A sintered ceramic is created from mixed powders. The ingredience are in solid form. Pressed into shape and then heated up under high pressure to bind the particles together to form solid part. Materials like Cobalt as used as the so called matrix which acts as glue. Its binds the other parts together. While sinter ceramics are pressed under high temperature this is usually still is way below the melting temperature of tungsten. So to really put the ingredience together you need something that at least gets soft and sticky. The matrix material can also provide other properties. In the case of Cobalt its elasticity. Which counteracts the brittle nature of WC.

This is why there is a difference between WC as a ceramic and W based alloys. Different methods of ceration and different matieral properties.
 

schnuersi said:

The M993 propably is a "victim" of modern engineering.

Well, the M993 was designed to defeat RHA (which is not really hard) even at shallow impact angle, so using a high cobalt fraction is sound engineering for me (WC with high cobalt fraction have a higher  transverse rupture strength).

WC with a lower cobalt fraction will be harder, but also probably less effective against the sloped armor of BMDs and BTRs (which were the primary targets of the M993).

Even if those numbers are difficult to compare (due to different test methods), the reported penetration capability of the Smk(H) is 13 mm / 30° of armor at 100 m, which is lower than the 18 mm / 0° of the M993.

Here is a comparison between the M993 core (WC cemented with Cobalt) and the WWII Russian BS-41 core (WC cemented with Nickel, like the Smk(H)).

https://www.researchgate.net/publication/310751663_Mechanical_Property_Comparison_of_the_Soviet_BS-41_and_the_US_M993_Armor-Penetrating_Cores

And an interesting presentation on the development of a 7.62 mm AP bullet, showing an open-jacket, tungsten carbide design.

https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2012/armaments/Thursday14062tran.pdf

The bullet was only 25.5 mm long, but could defeat >19 mm of RHA at 100 m. Now imagine the same bullet design, in .277" diameter, with a length >32 mm and increased impact velocity.

EmericD said:

It's because Nickel or Cobalt are not used to form an alloy with WC, but are used as a binder

Yes I had seen a number of WC Nickel binded ones. Whats throwing me off is the copper addition. 

That seems to appear only in various WHA alloys; I didnt see any copper options in the website you linked for example, just a bunch of WC-Nickel mixes sans copper. 

EmericD said:

And an interesting presentation on the development of a 7.62 mm AP bullet, showing an open-jacket, tungsten carbide design. https://ndiastorage.blob.core.usgovcloudapi.net/ndia/2012/armaments/Thursday14062tran.pdf The bullet was only 25.5 mm long, but could defeat >19 mm of RHA at 100 m. Now imagine the same bullet design, in .277" diameter, with a length >32 mm and increased impact velocity.

Thats an extremely interesting presentation, thank you for sharing that.

Based on that data, what would you predict for the increase in performance when going to the >32mm .277? 

And assuming a similar design to the one in the slide, and our previous 6.8GP projectile shape, what would you estimate for the projectile weight of this exposed tip tungsten core round? 

Thats something thats been troubling me - given how much heavier tungsten is compared to copper/steel, the AP projectile could end up being quite different in weight to our estimated 120-135gr for the 6.8GP EPR.

....

"Here is a comparison between the M993 core (WC cemented with Cobalt) and the WWII Russian BS-41 core (WC cemented with Nickel, like the Smk(H))."

I'd never heard of the BS-41 before, I'd be fascinated to see one tested by Buffman to see if the different binder changes performance against ceramic.

schnuersi said:

Because there also is a sintered WC sinter material with the same composition.

Is there? Because thats what I've been trying to find. 

Everything I googled turned up W90NiCu type alloys, rather than a combination of nickel + copper binding sintered WC. 

gatnerd said:

Yes I had seen a number of WC Nickel binded ones. Whats throwing me off is the copper addition. 

But they also found iron in the M993 core, while none is reported in the ARL-TN-0802 report... maybe some pollution from jacket particles? 

gatnerd said:

I'd never heard of the BS-41 before, I'd be fascinated to see one tested by Buffman to see if the different binder changes performance against ceramic.

BS-41 will be challenging to test!

https://apps.dtic.mil/sti/pdfs/AD1118640.pdf