OK, this is very, very hypotetical, but here we go:
Penetration of the M242 Bushmaster using M791 Ammunition(the old one, the new M919 is said to have even better penetration ability) is taken from:
http://www.atk.com/defense/descriptions/products/munitioncards/m791.htm
Penetration (typical): 25mm RHA @ 60º is 1300m
other sources say 27mm RHA, but 25 seems to be on the safer side. Also notice this is at 60°. At right angle(ideal) penetration is better.
The M919s penetration is classified, but some sources say 30mm@60° and 1500m, but that's just estimation..
Now according to
www.fas.org the BMP1 has 23mm turret and 19mm hull maximum armor -> M242 penetrates even with M791 round.
The BMP2 is said to be at 23-33mm maximum, which may or may not be penetrated, but remember this is maximum, a side shot will pierce the armor with M791, but the M919 might even penetrate from front(since it's ratings are classified who knows..)
BMP3 maximum armor is 30-35mm, which is once again not penetrated by the M791, but maybe by the M919; side armor is usually weaker and therefore will probably be penetrated by the M242 APDS rounds.
This is only true for the NAKED vehicle without add-on passive or reactive armor! Additional armor will decrease the probability of penetration, but adds weight.
Add-on passive armor as well as ERA(note: still no clue for heavy ERA) is available for BMP2(ERA only for BMP2D) and BMP3.
Since half of the information on this topic is classified, that's the best I could find, but it proves the M2's main gun defeats both BMP1 and BMP2 plus can penetrate BMP3s side armor unless add-on armor is present.
According to:
http://club.guns.ru/wwwboard/message/eng/810.html
The 30mm 2A72 gun of the BMP2 and BMP3 is not weaker than the M242, but more or less equal(compared to M791 rounds - M919 might be better..).
The AP-T
(BT) projectile weighs 400 g, contains 127 g of explosive
and is stated to be able to penetrate up to 18 mm of armour
plate set at 60° at a range of 1,000 m (25 mm at 750 m).
Penetration at the maximum effective range of 1,500 m is 15
mm. There is also an APDS-T variant with a muzzle velocity
of 1,120 m/s and an armour penetration capability of 25 mm
of armour plate set at 60° at a range of 1,500 m.
That's all I could find until now..
Snakeye
