Does the ammunitions AP mod. subtitude weapons AP or modifi it.

for example if i shoot hollow point rounds from a heavy pistol is it 6P/+1AP or 6P/+2AP

Becouse i think it should be the former but all of the tables in the books use the latter.(ie. shotguns)

The weapons in the tables ignoring this are... special. Or something.

All ammunition AP modifiers are just that, modifiers. They stack both ways positively and negatively.

So in your example the Heavy Pistol is 6P -1AP Hollow Point rds have a +2 AP modifier I think?
If so the final damage is 6P (DV) with +1 AP modifier.

Shotguns are an exception because they often use the flechette rules. There remains a question as to whether or not they should have a +2 AP or a +5 AP based on the new flechette rules from the SR4 1.5 Errata.

Otherwise, the AP modifiers for ammunition are just that: modifiers. If the weapon being used already has an AP value, modify that value by the value of the ammunition's AP.

Edit: Curses ... foiled!!

Thanks that what i thought, but i wasn't sure.

and magus Heavy Pistol is 5P -1AP and Hollow Point rds have +1DV +2AP.

@Max
Thanks I did not have a book handy for the Hollow Point rds. I have a player who was thrilled to see them in Arsenal. Until I explained them to him.