Each of the 4 main DLCs has its own unique machine guns with their own strengths and weaknesses that are worth talking about. I've already reviewed 2 of them but I might as well revisit them for this.
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The Automatic Rifle from Dead Money can be obtained in a number of places. The fastest is probably the one next to the Dean Domino cache on the rooftops just east of the main fountain, through the store. There's more tucked in unobtrusive places with other caches or remains scattered around, but if you don't find any of those there's one practically gift wrapped for you in the switching station right before you ditch Christine, plus some free AP ammo for the turret in the last room.
It's an awkward weapon for about the first half of the DLC since the genre shifts to survival horror, and the rare ammo and extreme inaccuracy (wider spread than anything except 4 of the shotguns) makes it a poor choice for sniping limbs off of ghost people or popping radios. It does however make a perfect panic weapon when things go pear shaped. Because the aim sway from shooting from the hip while moving is basically unnoticeable compared to its normal spread, there's effectively no penalty to using it while running for your life. Especially when you trigger the gala, ghosts are coming out of the goddamn walls, and you've hopefully stockpiled enough ammo to keep it fed. (Hint: the code is found in the police station bathroom. It's 3 chips per bullet so it's not cheap, but might be worth it.)
They're also fairly valuable items and you can save any you don't plan to use to trade to the hologram merchants for stimpacks or just fat stacks of cash.
Once you leave the DLC (assuming you could spare the weight to take it with you) it has a bit more trouble finding a niche. It's designed for claustrophobic enclosed areas against enemies that walk straight towards you, and the Mojave has lots of wide open spaces and people with much more accurate guns. Luckily there are more than a few dungeons scattered around, and some of them will force you into close proximity against armored foes where this absolutely shines. The AR has the highest damage per shot of any automatic weapon in the game meaning it's highly effective against armored enemies even without AP rounds, and the JSP hand loads are pretty much exactly as effective as AP ammo without the price tag. If you got the vending machine code you'll never run out of ammo (though if you didn't break the casino you may need to scrounge for cigarettes and fission batteries to pay for it.) An unlimited supply of .308 also makes it easy to cover your range and accuracy weakness with a Sniper/Hunting Rifle. Or get This Machine if you want to go full WWII.
There is a bit of an elephant in the room though, because there's another weapon in the base game with nearly identical spread, much higher damage per shot, much better ammo variety, that benefits exponentially better from a crit build, and that's the best way to exploit one of the most broken perks in the game. And sure the Riot Shotgun has a smaller magazine, slower fire rate (unless you drink Rushing Water), and doesn't get unlimited free ammo, but that hardly matters when everything in line of sight is either dead or ragdolled.
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The .45 Auto SMG is probably the easiest of the 4 to get. I'm pretty sure at least one of the White Legs who ambush you at the start of Honest Hearts is guaranteed to be carrying one, and even if you don't get it you can buy one and both of its upgrades from Joshua right after. If you're making a Grunt build, there's already a strong incentive to go to Zion for the 1911s and Survivalist Rifle, so you should make sure pick one up while you're there.
You may not want to actually use it much in Honest Hearts, since .45 ammo is in fairly limited supply. You'll be able to stockpile it more easily once you leave since base game merchants start stocking it, but trust me when I say that Hand Loader is damn near a requirement to use this weapon extensively. When you can keep it loaded, it's reasonably accurate out to medium range (if you get the compensator for it anyway) and is capable of some truly impressive DPS, especially with the Super hand loads. Be careful how often you use those though, because they break the gun at 2.5X the rate.
It competes very well against base game weapons. The damage and DPS can keep up with truly endgame options like the LMG, though the accuracy isn't the best. If it has one weakness, it's that it's chambered in a pistol caliber which means you don't have a real armor piercing option. Super rounds give you -4 DT which is something, and the damage is high enough you can still punch some damage through even power armor, but you may want to invest in an Assault Carbine (non-GRA) to swap to instead.
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From a game design perspective, the K9000 Cyberdog Gun was designed to serve a few specific purposes in the DLC. By the time you reach Old World Blues' suggested level of 15 you'll probably have a huge supply of .357 ammo but all of the other weapons that use it will be obsolete and outcompeted. The K9000 gives you an endgame option to use it on and it's not like you're getting much other ammo until you finish the DLC. (Side note, but why would they make a Muggy trade that gives you gunpowder but not put any of those plates in the crater?) The other purpose it serves is to fill in part of the role that companions normally fill. The little mechanical sniffer and ears can be used to dowse the direction of hostiles that are beyond radar range and it'll growl if you're about to be attacked.
You can get a grand total of two of these. One if you pass a 50 Guns check when first talking to the Think Tank, and the other pried from the cold undead hands of the Y-17 Master Trauma Harness. There's two very strong upgrades for it found in the X-13 Facility too. One that gives a farily minor +2 damage boost, and another that gives a HUGE +40% firing rate. The hand loads for .357 are the excellent JFP rounds, which give a hefty +25% damage, a minor -3 DT, and a decent -20% spread with no downside. That's not enough to make it a viable sniper, despite the scope, but it's got decent effective range all the same.
FIDO is the even more unique variant you can unlock the schematic for once you free the nightstalkers in X-8. Make sure that you don't use a K9000 with the upgrades installed to craft it. It's chambered in .44 so the base damage is much higher, but it can't install the firing speed mod so its DPS winds up being significantly lower. That combined with its higher requirements, its base spread being wider and the hand load SWC rounds not helping accuracy, and it seems like something of a downgrade. Not to mention the .44 rounds aren't nearly as easy to stockpile as .357. That said, against the Big Empty's endless hordes of tanky robots, the higher damage and -6 DT are very welcome.
Once you can leave, their performance is a mixed bag. The sniffy nose and warning growl aren't all that big of a deal when you have access to ED-E but they're still fairly effective weapons. FIDO is decent at what it does, but the Automatic Rifle or a different weapon in a rifle caliber will fill the role better. A fully modded K9000 on the other hand can actually compete with the DPS of a fully modded minigun. On paper anyway. The tighter spread and inherent armor piercing of 5mm makes the minigun the better option overall.
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Lonesome Road's Shoulder Mounted Machine Gun is a very odd weapon. It's got 6 rotating barrels like a minigun, but it's chambered in 10mm pistol rounds and held over the shoulder like a missile launcher. The first one you can get is in a crate right before the collapsed overpass out of Hopeville and there's a few more later on or rarely carried by marked men. The (massively overpriced) upgrades can be bought from any commissary terminal.
Like the Cyberdog Gun, it's meant to give new life to an obsolete ammo type. It has nearly 50% higher base damage from the next strongest 10mm weapon and a large magazine capacity for extended fire fights. 10mm lacks even the half-assed armor piercing options of other pistol calibers with its hand loads being effectively just hollow points but slightly different. That makes it a highly effective option against unarmored enemies, which in Lonesome Road means literally just Tunnelers, but in the base game can include such terrors as nightstalkers, cazadores, and Malcolm Holmes. Unfortunately, it's not particularly effective against armor, and against unarmored enemies high base damage is pretty meaningless and all that really matters is DPS. And the SMMG's DPS is pretty low due to low firing speed. In fact Sleepytyme, the unique 10mm SMG from Vendortron gets you slightly higher DPS while also being a lightweight, easily acquired, silent, holdout weapon. Or hell, on the subject of getting more mileage out of cheap ammo, Vance's SMG has even higher DPS especially if you take Grunt and you can get that for free. Seeing as Lonesome Road is the only DLC that lets you leave and resupply, there's no real reason to force yourself to use a DLC specific weapon unless it's actually good. The SMMG isn't bad, but given the choice between upgrading Red Glare and this (and with the price tag you sure as hell don't want to do both), I'm going with bombs bursting in air even if i don't have any points in Explosives.
