How about two weapons?

Oops, forgot to mention my personal choice for concealable weapons for dealing with cars ... the 40mm Grenatepistole (HK69), or any of its cousins - including the venerable M79, especially in sawn-off version. Loading a nice HEAP warhead they'll take out a car with gratuitous ease - while loaded with a buckshot canister, they're a hand-held Claymore mine ...

Heh. If we're talking about grenade launchers, you might also want to check out the M-203 grenade launcher, which is best used when attached under the barrel of an M-16 or one of its later variants.

It's mainly Ex-Special Forces fare, but a Killer or other gangster type using one of these isn't unheard of -- witness Tony Montana's final stand from SCARFACE ("Say hello to my little friend!") in which he uses both the M-16 and the aforementioned grenade launcher to deadly effect against a good-sized army of seriously well-armed assassins.

Ah, but the M203 requires an M-16 to be mounted under. The M79 is the precursor (as waved around by big Arnie in T2, with the distinctive 'bloop' firing sound due to the low-pressure cartridge). It has the advantage that, with its own stock, you don't need to hide the rifle too ... The sawn-down version, with the wooden stock reduced to a pistol grip and the barrel cut-down too, was used in the Vietnam war by regular forces as well as the Montagnard allies - the shot cartridge held 20 buckshot, and was fairly effective at very short range as a quick response to ambushes in the jungle. Even if using the standard grenade, which doesn't arm within 30 metres, you can still kill or disable if you actually hit a target with the round. (Bless Wikipedia for the stats!)
A sawn-down M79 or its more modern replacements (the HK one mentioned above) would fit in a briefcase or shoulder bag, or under a trenchcoat, rather more easily than the M16/M203 combination - handier for those urban hits when one needs to make a big bang to get in or out ...

There are actually aftermarket stock assemblies for the M203 which would allow it to be used separate from the rifle. Though frankly the HK69 looks better and its break-open design allows it to fire longer rounds than the M203. I have used it on several occasions (or at least my characters have). As for the Barrett, the XM109 FYI, she was able to conceal that thanks to a cunning (and somewhat munchkin) combo of the homebrew schticks Trenchcoat and Bag Full of Guns which basically allowed her to pack a theoretically endless arsenal under an unassuming topcoat.

Fair point!

Heh. Cunning. Then again, have you seen Gunsmith Cats? There's a Russian assassin with a greatcoat like that ... in one scene she hangs it on a peg, and as she walks off you see it rip the pegs from the wall ...

I haven't actually (not as up on anime as I'd like to be). But I had the vague sense when I made the character that I'd read about something like that being in some anime or other. Of course in play I kept breaking out the craziest, most improbable weapons I could think of. The other real highlights were an RPD light machine gun and a pair of S&W .500 Mags.

[color=darkblue]On a totally-unrelated-to-Feng Shui note... when I played in a friend's Star Wars campaign a decade ago, I had a Quixotic Jedi archetype. I wanted him to have a non-lethal weapon, so I glanced down the weapons chart and picked a "riot gun" stun rifle. It did only stun damage, but it did a crapload of it, so I was almost assured of removing opponents without killing them.

Now, I was thinking of a riot gun in terms of a shotgun-like thing, designed for two-handed use by one man. It wasn't until about two games into the campaign that I read the actual description, and realized the riot gun was a monstrous, tripod mounted thing! :unamused:

The GM ruled that I had a specialized, smaller version of the gun, and reduced the damage a bit, but from then on it was a running joke that my Jedi would meet some opposition, and from beneath his flowing cape, yank out this humongous behemoth of a gun...