AP use confusion

[jivemi]

Basically AP and APCR (aka APDS) depend on velocity so their penetration value decreases with range, while HE and HEAT depend on explosives in the warhead so penetration is the same at all ranges. AP Calc tells you what you can expect at various ranges with different guns using AP or APCR; you may notice that penetration often declines drastically as range increases.