My bold - I don't know, but I do know that gun barrels are very high quality steel, hence we still retain 105mm tank gun barrels for testing etc not because we still have some Cents squirreled away somewhere.Slope means nothing these days. I've got a document from the 60s with RARDE stating they've improved APDS to the extent it'll work on high slopes, IIRC 70+ degree's. Plus, I wonder if a gun barrel is actually hardened as armour?
Some modern armours work on producing sheer forces into the penetrators. This causes the shot to break up inside the armour. I've been told there's been some work around that with some interesting ideas in regards defeating that sort of protection. No idea how true it is, as for some boring reason modern armour is really classified.