and it's pure BS.
DM53 out of L55 gun is frankly enough to penetrate any russian tank, the problem is probably the Kontakt-V that will break the arrow before in can penetrate. Some areas of turret on T-72B/T-90/A and T-80U are indeed unpenetrable, but most of the frontal aspect of the tanks are less protected.
DM63 is for 105mm guns, the article is total BS they don't even know what they talk about.
Russian experts rate the 120 L55 with DM53 as the most powerful anti tank system in the world, on equal footing with 120L44 US firing M829A3.
But that was before 2A82-M1 with new APFSDS rounds, which, might be the uber most, but, are not fielded yet and won't be until 2018 at least.
Russians rely on tungsten too... Only US and china went full retard with DU rounds, most countries have a small number of DU and mainly use tungsten.