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

EmericD said:

maybe some pollution from jacket particles?

That definitely could be a possibility; likely more probable than my nazi time traveler hypothesis for how they got advanced WHA cores. 

gatnerd said:

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

You can find WC in a Fe or Cu matrix nowadays. Usually not mixed. They are not that common and only used for special purposes.
But keep in mind these are modern day materials for tools. Not old special compositions for military purposes.
Its entirely possible, as well as the contamination from the jacket theory, that the WC in FeCu matrix material is special for penetrators from Germany of that time.
It also makes sense to use Fe and Cu instead of Co from the German perspective of the time. The SmK(H) had been intended for wide spread use. The original idea has been to issue one or two strips of it to any rifleman. The intend being to turn any rifleman into an AT-rifle gunner. Fe and Cu is rather easy to come by. Co is needed to produce tools. While W also has been difficult to come by at least this way they could save Co.
Again its most likely a combination of several factors.

EmericD said:

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).

This is exactly what I mean.
Yes its sound engineering from a modern point of view. As you mention the M993 has been designed to achieve a specific level of penetration against a defined target at defined range. It has not been designed to deliver the maximum possible penetration from a standard issue rifle.

EmericD said:

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.

Well that depends of the 30° are measured against the horizontal or vertical. 
12 mm at 0° against armor steel (what ever this exactly is) is usally found as the penetration for the stell core SmK in German sources. That is allready awefully close to the performance of the M993.
The numbers given for the SmK(H) are conciderable higher, As high as 20 mm RHAe at 500 m. Which I find high but not impossible.
If your penetration number is measured against the vertical, as has been done back in the day depending on nation and time, the penetration with 0° impact would become 26 mm. Which is really quite a lot but consistent with the performance of the 7,92x94 Panzerbüchse ammo. Which does roughly twice that with an allmost identical Smk(H) but at higher velocity for a little more than twice the KE.

schnuersi said:

The numbers given for the SmK(H) are conciderable higher, As high as 20 mm RHAe at 500 m. Which I find high but not impossible.

Thats really pretty remarkable. Nammo's current .338 is rated for 12mm @ 550 - 600m

https://www.nammo.com/product/our-products/ammunition/small-caliber-ammunition/8-6mm-series-338/8-6-mm-x-70-338-lapua-magnum-armor-piercing/

On the other hand, the SMKH did outperform the .338 249gr AP load @ 100yd. SMKH punched through the plate cleanly at 100yd, and exited the clay backing box. .338 penetrated roughly, and its core (or core fragments; unknown) was caught in the clay box.

https://www.youtube.com/watch?v=CdRFYmPmetc

At 100yd, the .338 had 3,655ft/lbs of energy vs 3,700ftlbs for the SMKH at the muzzle. 

It really is a beastly penetrator.