120mm Ammo used by...

[Marcello]

I have further looked into the M830/M830A1 issue.
There seems to be a "expert" consensus that M830A1 sacrifices a lot of penetration potential in order to achieve other effects, with penetration estimates as low as half of that of M830.
That being said M830 was still issued during OIF and beyond according to US tankers, so it might be used to avoid the apparent contradiction of a decreasing HEAT value for more modern US guns.
In regards to APFSDS the thought seems to be that M829A2 pretty much used up most of the remainin growth potential of the M256 gun in terms of "raw" power (maximum pressure etc.).
M829A3 and M829E4 play around the margins with improved materials, shapes etc probably to improve performances against advanced reactive armors (Kontakt-5,Nozh, Relikt etc.) and similar threats but with only relatively modest improvements against a RHA target.