How good were these rounds in actuality, in game they perform well against most opponents in its battle rating, but the effectiveness of these early L7 rounds is debatable.
The shattering mechanic that Gaijin attempted to revive has some truth to it allegedly, and while the penetration statistics in game are probably accurate, in function these rounds may have had trouble penetrating sloped armor. Israel, India and Pakistan have probably used these rounds the most, with the Six Day War, and Yom Kippur War, Centurions armed with this gun performed well, and they would have been most commonly equipped with L36/L28 APDS. On many instances this gun were taking out even T-62s/T-55s but not necessarily from the front and not necessarily through the hull. I cant find many if any frontal penetrations with the images I have looked up (not even signs of hits, suggesting they were told to aim for the weaker turret) and in fact seen an image of an IS-3 take many hits from alleged L7 APDS which it doesnt have much trouble penetrating in the game.
I did find an image of a T-55 frontally penetrated by what looks like 105mm APDS. 105mm did not have APFSDS rolled out until 1976, and that is definitely not HEAT so if you connect the dots 105mm APDS is most likely.
In game L28 APDS has:
up to 350mm at flat
up to 135mm at 60o slope
There are variations in testing reports where the flat penetration is much lower and the sloped penetration is slightly lower. Given the IS-3 was indeed shot by this round then unless it was performed at an extreme range then for whatever reason these penetration figures were not accurate that day.
Something to note was that this ammunition was designed to defeat T-54s and of course, roughly 120mm at 60o is enough to do that out to reasonable range, which is the most commonly stated figure in testing reports at round 1000m.
I mean look, everyone and their mum used this gun and still use this gun religiously, presumably its first ammunition type was good enough to attract so much attention.