Requirements:

Base Fallout
(I don´t really know this) GRA
And the Handloader perk

Install: 

Just normal, either just install it with the NMM, or put the .esp in the data folder.

What it does:

It adds one armor penetrating round-type to:
10mm
12.7mm
.357 Magnum
.44 Magnum
9mm
45-70 Gov´t
.45 Auto (maybe, as sometimes it works, sometimes it doesn´t, I don´t know what causes this inconsistancy)

All the Bullets have these specialities:
Damage x0.95 (except the .45 Auto which has  x0.8)
Damage Threshold -15

Please Note: All of the recipes require the "Handloader" perk.
   All the bullets must be crafted. (The costs are slightly higher than the standard rounds)
   All the fired bullets have a 10% increased chance to drop hulls

All the ammunition is properly implemented, meaning that they also work with added weapons as long as they stick to the G.E.C.K.´s Form Lists.
Obviously the bullets can only be crafted at a workbench.

Why:

I was fooling around with a build that focused on small caliber firearms that use 9mm, 10mm, .357 Magnum and .45 Auto.
And although there is a +P (Increased Pressure) ammo, there was no Armor Penetrating round, so I made and implented them.
Believe me, it´s no fun trying to kill a Deathclaw (Base DT:15) with measly +P rounds.


Incompatibilities:

There shouldn´t be any, as long as they don´t reassign weapons to new/other Form lists.
Oh and the occasional auto-blocking which causes the .45 Auto AP round not to be implemented.

Cheers.

Edit: Just a little info: the creating of this mod took about 4-5h because i had to test it thoroughly. (Maybe it was caused by my own incompetence)
If you use my mod in one of your own mods, please put up a thanks message somewhere.