Thanks for the responses!
Just to get a bit more specific, two of the sessions I listened to were using A Dirty World, an indie game centered around the film noir genre. Its fairly rules light but features an emphasis on contested checks between PCs as well as against NPCs. The idea is that you can affect the motives and resources of your corrupt(ible) associates so as to gain influence over them. The fact that both sessions were One Shots (though they may have followed up on one of them) is important to note, as well.
Something else of import - there was a lot of scene switching, with the GM alternating between particular PCs or small clusters of PCs getting up to nefarious hijinks. While the other players were aware of what one particularly backstabbing and greedy S.O.B. PC was up to, they seemed to do a decent job of keeping that knowledge OOC and not dragging it into their interactions with the guy In Character. I think it may be a play style that some players would not appreciate ("Aren't we ever going to meet and do something TOGETHER?"), but it didn't seem to drag on too long in any given scene and people were at least amused by other players' antics even if their PCs weren't present to contribute.
I think there was maybe one
actual attempt by a PC to get another one killed in the two sessions total, but there was still a lot of undermining and backstabbery in a less literal sense going on. In one of the two, a straight-laced sheriff PC was manipulated by an amoral criminal defense lawyer PC, an ex-con PC covered up some crimes he got into to conceal them from both the lawyer and the sheriff, and the sheriff and ex-con were both maneuvered into moving against the main "bad guy" NPC by the lawyer PC. The sheriff and ex-con got into a gunfight against the bad guys, and the sheriff was killed despite the ex-con's attempt to save him. The lawyer walked into a shotgun ambush set up by one of the innumerable people he screwed over during the adventure, which the provocateur player seemed to think was totally appropriate.
Now, obviously, Ten Thousand Bullets and Mastercraft aren't meant to do all the same things as A Dirty World or ORE. I LIKE the distinctions between them and would probably find different kinds of things to do with them if I tried to run both. However, I kinda think a gritty kind of tale of backstabbery and set-ups would not be far afield from 10K's wheelhouse.
To throw out an example from the crime story genre, how about Heat? If we take the tack that the heist crew are the PCs and the cops are NPCs (though the idea of an improbably crazy big game with PCs on both sides is kind of intriguing), then we see that these guys work well as a team - aside from the one serial killer guy, who we may assume is an NPC foisted upon them by a mischievous GM. They pull their jobs off with military precision and have disciplined themselves to be professionals in their field. They may even be kind of friends with one another, hanging out as they do with each other's families. They are, in other words, kind of like most traditional PC groups.
As the story progresses from that first armored car job, though, things start to fray at the seams. Contacts sell them out, the cops come down hard, and even one of the team's loyal members sells them out (Danny Trejo's character) after being tortured nearly to death. By the end, only Val Kilmer's character gets away, and even he has to deal with being wounded and abandoning his wife to police custody.
Assuming that this was a 10K campaign, would it be a success? If you were Danny Trejo, would you punch the GM in the face for killing your PC's wife in a Torture dramatic conflict? Would Bobby DeNiro be happy with how his last minute change of heart to avenge his friends got him killed by that Al Pacino cop NPC?
Personally, I'd say that if the group knew going in that it could all Go Bad in a big way, they might feel satisfied. Maybe. It'd ease the pain a lot if it had been a One Shot, but maybe it had gone a few make-believe sessions before the finale. It is, after all, a crime story, and those tend to end poorly for the crooks. They even end bad sometimes for the cops. Consider L.A. Confidential, a movie with three very PC-like protagonists, only one of which walks away relatively unscathed. Er - spoilers, but if you haven't seen that movie by now, I can't help you.