Also, round still has more muzzle energy than 3BM42M Lekalo (tanknet calculations assume projectile weight as 4.85 kg i.e equal to Svinets and say that muzzle energy is 7.4 MJ)
You are comparing apples with bananas. We need to distinguish between three different values:
1.) projectile (projectile assembly) - the projectile assembly consists of the in-flight projectile and the sabot.
2.) in-flight projectile - the "dart" which is kept in place by the sabot. This also includes the weight generated by tip, fins and tracer.
3.) penetrator - only the heavy metal rod inside the in-flight projectile
The differences between these weight values is fairly large. The U.S.-American M829A1 APFSDS for example has a 9 kg projectile including sabot, but only a 4.6 kg penetrator. The Russian 3BM-42 Mango APFSDS has a 7.05 kg projectile assembly, which consists of 2.2 kg sabot and a 4.85 kg in-flight projectile (andless than 2 kg penetrator). The muzzle energy of the 3BM-42 projectile is 10 MJ and 7 MJ for the in-flight projectile. But the energy effiency (how much of this energy is actually generated by the penetrator) is worse than on most other rounds due to the projectile constructor.
For the Indian 120 mm APFSDS there is not enough data to calculate the penetrator energy.
Can you please use the Lanz-Odermatt or Andersen equation to calculate the penetration?
Based on the very few images actually showing the Indian 120 mm APFSDS it should be about ~480 mm long and have a diameter of about 28 mm. It seems like there is no public available source stating the deceleration (decrease of velocity), so I'd assume it would be 60 m/s/km (for reference, DM53: 55 m/s/km, M829A1: 65 m/s/km).
Such an APFSDS would then end up with a penetration of 430 mm into a 235 HB plate sloped at 60° at 2,000 m or 367 mm at 0°.
235 HB is however very soft steel, as used on the Patton (M47, M48 & M60) tanks. The Soviet T-72 uses reportedly 270 HB steel - then the armour penetration would decrease to 405 mm into a 60° sloped plate at 2,000 m and 347 mm into 270 HB steel at 0°.
Getting boring editing stuff[/B] DM13 penetration at 60 degrees is 230. How much at 0?
This value comes originally from Stefan Kotsch's website, who was a member of the East-German and later of the unified German army. The problem here is that DM13 is a very old round and it's construction is not very advanced (it is no monoblock round). Depending on the tip construction it would penetrate about 400 mm RHA at 0° (if the tip is good constructed, it will increase the penetration against sloped plates) or ~440 mm at 0° (if the tip is bad constructed, it does not increase the penetration by much, see old Soviet APFSDS for reference).
Remember that Chinese Type II M penetrates only 220 mm at 66 degrees but 550 at 0. (How? 3BM42 Mango penetrates 220 mm at 60 degrees - not much of difference isn't it - and still certified penetration is 450. Yes I know it can penetrate 500)
220 mm at 66° equals 540.8 mm line-of-sight. 220 mm at 60° equals 440 mm line-of-sight. Maybe both rounds use rather disavanced penetrator/tip construction, which does not enhance penetration against sloped targets?
Also, (Keep forgetting) Is this page reliable:
http://echo501.tripod.com/Military/120ammo.htm
It's a website made for wargaming. It isn't reliable, you can find hundred such sites in the internet. Most don't use any reference, but if they do they often reference random forums.
). 
design better tank?
