For anybody needing proof that greased rounds on the gat is actually a terrible idea:
Greased + Buff
Per shot: 16.32
Per second: 163.2
Per clip: 1175.04
Heavy + Buff
Per shot: 17
Per second: 127.5
Per clip: 918
Difference (Greased - Heavy)
Per shot: -0.68
Per second: 35.7
Per clip: 257.04
Now, how do those prove that heavy is better? Miss two shots per second with greased, and the advantage per second shrinks to 8.5 and the advantage per clip to a rather unimpressive 61.2. If you miss three shots per second, then you're doing less damage than heavy.
Find a situation where you can get up to point blank against a ship where the profile is large enough to land enough hits, while also ensuring that none of your rounds go into their guns/engines. Then you'll have a valid use for greased gat.