Interesting ,I was under the impression that the American 76mm was at least comparable to the 17 pounder (which in game has more penetration in game)
FH refers to performance against face hardened armour and this is on USN pen standard so 50% chance of full penetration on the indicated value.
17pdr:
76:
Kwk40:
why does the jagdpanzer IV have 12 AP XD
L46 is the towed PaK 40. L/48 is used on pz.iv G and stug III G onwards. The 17 pdr was not liked by the US when they tested it against their 76 for a bunch of reasons... I wouldn't really call their pen comparable tho