The P12 is described as:
A tactical pistol for stealth kills.
It’s located north-east of central Tabacal province, near some train lines in the middle of nowhere, with a Sicario Leader side mission nearby. The weapons case is next to a huge rusty pipe under a covered roof.
There are six sicarios and the sicario leader here, which are easy to take down, but difficult if you intend to intimidate the sicario leader.
This pistol, along with the M9, 5.7 USG and P45T achieve maximum noise reduction for the stealthiest close up kills. It has a 12 round standard magazine and accepts the same 20 round .45ACP extended magazine (found in Koani) as the P45T.