I have a book from the Tank Museum, in Bovington UK, which states that the Sherman Firefly could fire APDS, yet it does not in-game. Book: Tank Spotters Guide

[[email protected] 0]

[TheNexonRegime 423]

One of the Italian Fireflies can use APDS.

[Valcour 1,131]

Balance reasons no doubt.

 

[Headnaught 488]

As Valcour said that is most likely the case. The British Army began issuing APDS rounds for pretty much anything equipped with a 17-pounder or 6-pounder in order to have better anti-armor capability against the heavier German tanks they encountered. It's completely at Gaijin's discretion to provide or withhold ammunition, otherwise Churchill IIIs, Cromwell Is, Avengers, Fireflies, etc., would all be running APDS.