You should approach the problem a little more realisticly. Do you need a perfect masterwork, barrel and mag? Or can you do with almost every barrel anyway because it doesn't matter too much (unless pulserifle)? That being said, it is still depressing sometimes. The dungeon weapons are terrible in this regard. I farmed myself a Last breath from the cube room in prophecy. 1/36 for the last 2 perks, 1/3 to get LB from the encounter makes it a 1/108 chance per encounter and this is one of the better ones when it comes to the odds. Should you want a specific last 2 perks of No survivors, you can do 1st or 2nd encounter in Ghosts of the deep for a 1/6 * 1/36 making it 1/216 chance per encounter. Should a weapon roll require column 2 as well, then everything is lost: Cataphract is a 1/49 for envious +B&S and you need spikes (another 2/7) makes it a 0.58% to get the roll (not talking barrels or MW). You can imagine the amount of trials resets for this on average for yourself. I also farmed for a Lingering dread with holster, chill clip and disorient with no luck. 2/5 for the disorient, 1/36 for holster+chillclip Then either 1/5 in the first encounter or 1/11 with Caiatl. There is also this terrible ruling where master caiatl cannot drop the thing (as opposed to normal) so you cannot get to farming this alongside a more efficient artifice farm. And you can always be unlucky and crash the average amounts without getting one.