OTL the Germans reached the Channel on the 19th.
ITTL on the 21st there have "only" reached Montcornet.
Does this delay allow the Allies to pull back from Belgium ?
For the 2 pounder : 37mm ( 60° ) at 500 yards(457m), using an AP round
For the 47mm : 40mm at 600 meters.
Source : Bird, Lorrin; Livingston, Robert (2001). World War II Ballistics: Armor and Gunnery
http://www.atf40.fr/ATF40/char%20B/armement.pdf