DU has far lower melting temperature than even ancient RHA, making it completely useless against any sort of HEAT munition.
What has melting point to do with anything?
HEAT warheads don't melt their way through armour... a HEAT warhead has velocity and density... velocity comes from the explosion and density comes from the material used for the cone of the warhead. DU armour is effective because it is dense and hard. In comparison Lead is pretty useless for armour from high velocity penetrators because it is dense but also soft.
In terms of penetration HEAT penetrators are treated pretty much the same as APFSDS penetrators... the difference is that the former is not as hard though the science of looking at penetrations at these velocities is fluid mechanics... treating hard metals like they were slow moving fluids, while the latter are hard but also moving much slower than the average HEAT warhead.
I personally would not include DU in armour, because I don't particularly want three heads and webbed feet for my grandkids... or anyone living near the combat zone.
And in that incediary effect DU becomes dangerous because it becomes radioctive when ignited.
DU is always radioactive. When ignited it burns to a very fine powder which makes it very ingestible... and therefore very very much more dangerous to humans and nature.
No matter how dense it is the low melting temperature radioactivity of ignited makes it useless against incendiary or HEAT weapons.
Modern armour structures consist of a range of materials including hard and soft materials... even including empty air pockets.
Most metals can ignite depending on the circumstances... iron powder is used in thermite, and aluminium powder is used to make the bright sparks in fireworks. Magnesium obviously burns as does lithium and anyone who has worked hard metals like Titanium will attest to the showers of sparks that come off it when cutting it with a high speed rotary tool.
Not true. Soviet DU rounds were just an experiment and for good reason. Unlike the americans they actually care for the health of their crew and limiting nuclear waste dispersal.
Even the R-60MK uses DU in its warhead... they don't use them much because of the costs of cleaning up afterwards, but they do have them.
The velocity defacto is not responsible for higher accuracy but a longer barrel undoubtly is responsible for higher accuracy. The RPK-74 also fires more accurate than AK-74 despite being essentially the same rifle except the barrel is heavier and longer giving higher velocity and accuracy and therefore higher lethality.
The increased accuracy of the RPK-74 over shorter barrel modifications largely comes from the fact that it also has a heavier barrel and a bipod to support the firing position.
The AKS-74U is evidence that if you shorten the barrel too far you can dramatically effect accuracy in a negative way, but we are talking about APFSDS rounds which are certainly not as accurate as full calibre rounds.
The US Army had extensive tests for weapons to replace the M16 and 5.56mm cartridge. One of the most fun contenders was from Steyr and it fired a flechette... basically an APFSDS round. the rifle had fixed iron sights because the enormous muzzle velocity and small low drag projectile meant you didn't need to correct the elevation for range to about 800m so elevation was fixed... aim at the targets chest and fire... from 10m to 800m and you should hit the target.
two problems... wasn't particularly accurate even if there was almost no bullet drop, and it wasn't particularly lethal... unless it tumbled and fishhooked it make an ineffectual puncture wound.