Having played several games against a mech grey knights player I can state that Fusion guns for the win! So many times my rail guns have been nullified by facing 3 land raiders and 2 rhinos hiding behind the LR's. Now a game like that I have 3 broadsides and two railheads. In terms of fusion guns I have my team leader with a Helios pattern load out and two teams of 6 stealth suits with the team leader armed with a fusion blaster in each.

I find the infiltrate to be a savior against this guy as I can then place my stealth teams to best advantage after deployment. If I have the advanced knowledge of fighting this guy I take a monat with the Sunforge load out ( correct me if I am wrong but I believe that is the name for the twin linked fusion gun) combine him with a shield and he has more than made back his points. In fact the two stealth teams and that single monat have accounted for more vehicle kills than my railheads and broadsides combined.

I don't use Piranha against him as he stacks his back line with psy cannon and heavy bolsters and even moving flat out etc they are usually toasted before they can get a decent shot in. Since the optimal use of piranha is a two unit the points I save there pay for essentially one of the stealth teams and the rules for targeting them
along with the 6 man team means my fusion blaster lasts longer.

While all that is a tad off topic, the addition of those 5 burst cannon in each stealth team I can still pump out 15 S5 AP5 shots each team plus one fusion shot per shooting phase assuming none of the team are killed. If both teams support each other then you can force a LD test on even an 30 boy Ork mon in one turn of shooting with good rolls. By then tactically using the J-S-J tactic and withdrawing back to your main line you can draw put the troops for better shots from the rest of your force.

Just got all my dudes massacred by an army that gives me The Fear. Also, nightmares. The nid close combat horde. Gaunts and 'stealers as far as the eye could see. My worthy opponent could barely fit all of his gribblies into his deployment zone. Only the monstrous creatures had any kind of ranged weapons.
So I did what any tactician would do; hid in a corner and had a good cry.

Once I had been found and dug out of my hole, he proceeded to steamroller his massive wall of chitin and blades down the table. My kroot held up two... broods (are they called broods?) of hormagaunts for a turn, but that didn't make much difference when there were four more maximum sized mobs of alien horrors.
Battlesuits, which I admit are currently optimized for dealing with MEQs as my regular opponent normally plays dark green mreens and this is what I was expecting to face, armed with rifles and rockets proved mostly ineffective. Burst cannons and flamers will be acquired with speed, as will more stealth suits which I plan to run at maximum squad size with minimal equipment (18 5-5 shots, yes please).
B'sides were moderately effective at whittling down his Tyrant and other synapse creatures. I need a railhead for the large 'splosion.

Most of my dudes were overwhelmed by sheer weight of numbers by the end of turn four. The only survivor was my deathsun Monat, who had the sense not to deepstrike onto the table until turn three, blasted/melted a thrope and then hid in the enemy's deployment zone where it was too far and too late for him to turn the horde around and hunt it down in time.
One case of battlesuit psychosis coming right up for that dude.

Painful, painful loss for me but some lessons learned. Mostly about how to paint up massive horde of 'nids and keep it an absolute secret to everybody.

I've got to say that Tau have a few some pretty decent anti horde in the following units-

Firewarriors- Their guns have good enough stats to bypass GEQ armor and wound on 2+; the only thing hurting them is their mediocre ballistic skill. With a few markerlights you can significantly improve their damage. The main problem is that they only get 12 shots (generally) but a devil-fish boosts their firepower considerably.

AFP Battle-suits- Large blast that wounds GEQs on 3+ and denies saves. Not too much more to say, except that it has a somewhat limited range, but a battle-suit has sufficient mobility to escape most attackers.

Railhead- Large blast that wounds GEQs on 2+ and denies armor. The cover will be a problem, but baiting an enemy out of cover is generally easy.

Stealth suits- Burst cannons put out enough fire to really hurt most units, and they are quick enough to avoid retaliation.

And obviously Heatwaves, which shouldn't need much arguing for; Twin-linked flamers will put down most anything with a bad armor save.

Fire warriors are the most point efficient unit we have for simple number of shots... with pulse rifles, you're paying 5 points per shot within the 12" range mark, so using them in conjunction with markerlights to boost shooting ability, and screens to ensure multiple rapid fire phases, you'll have little problem wiping the floor with the small fry. Piranha squadrons of atleast 2 bring maximal space coverage with armor protection, for what is arguably the best point cost, and it comes with a secondary screen in the form of gun drones to really hold back the tide, and equipping them with flechettes does wonders in denying an assault. I don't advocate a tailored list usually, but if anything holds back a tide of chitin, its flechette piranhas.

2 maxed fire warrior squads often does more than enough damage per turn against these lists, especially if you have a devilfish transport to ensure they get the first round of rapid fire. they'll very often clear out entire squads with marker support in close range, so ensuring they get as many rapid fire phases as possible benefits you exponentially against these lists.

Between kroot (which you should be fielding as screening units anyways) and Piranha squadrons (which you normally field to screen against vehicles and block narrow chokes to delay enemy vehicles, but against hordes sit in the way of the kroot) you should have plenty in the way of anti-horde firepower. By and large kroot units serve as your own "mini-horde" and can function quite effectively against them. Moreover, they put out enough attacks in CC to still threaten these types of units whereas your fire warriors (and the pathfinders you used to provide their markerlight support) will roll over and die once the gap is closed.

When it comes down to hordes you need volume of fire, and Kroot put out more shots per point than Fire Warriors do while also serving a more useful purpose when fighting other types of armies (namely, screens for your crisis teams).

And remember, if you're using screens to protect your fire warriors while they shoot (as suggested above) then you're providing the units you're firing on a 4+ cover save (for firing through a unit) making the superior AP of the fire warrior compared to the kroot useless. And if you aren't screening your fire warriors than you won't get enough turns to fire upon them before they close the gap and kill you.

The thing about fielding pirhana.... I cannot overstate how much I hate the models. I recognise that they would fill a vital battlefield role that I am completely lacking in right now (mobile area denial)... but I hate them sooo much and refuse to buy any. Bobsleds with jet engines, no thank you.

My defeat was ensured by coming equipped for bear but coming up against... something smaller and faster than a bear, but lots more of them. Wolves?

I know for a fact that I will also be facing eldar and orks in the near future, so I'll probably end up building an all-comers list - which is more of a personal funds issue than an army composition thing.

Basic firewarriors. Lots of them, I think. In pod'fish. Pretty safe bet.

Just a word of caution for you when building your list.

Fire Warriors are somewhat of a paradoxical unit. They're somewhat fragile (T3/4+) so you want to protect them, so you put them in a Devilfish to keep them alive so they can do their job. But then the Devilfish doesn't have any fire points so all of your fire warriors need to get out, losing the protection of their Devilfish for at least one turn.

You always have to choose between letting your fire warriors do their job (and they're too expensive to bring more than the minimum of them and not try to use them) or let them survive in order to capture objectives later in the game.

I don't understand what so many people have against fire warriors! Two ten man squads with a shield drone, markerlight drone and shas'ui each is about 140 pts apeice. For hordes, that in a ruin (with or without a fish) is nothing short of traumatizing. against orks, blow them apart before they get into combat, verses 'nids the same, versus hoarded IG infantry you have a 50/50 chance of surviving any wounding shots and they have to move into range of you for a turn, statisticaly, if you bring down *Maths noises* quite a few! I fully agree that a hammerhead is very valuable, just don't run as many crisis suits as most people do! They go down a lot easier than most people seem to assume. A list of things from a simple SM army that will ID them: Missile launcher (free for 10 man marine squads), power fist (still pretty common), Lascannon (your likely to see at least one or two), meltagun (same as lascannon), multi-melta (not as common, but does the same thing) and dreadnought (once again at least 1 in most SM armies)
Spare a little thought for the fire warrior, they need love, care, attention, and a bit of CC training.

Personally I never take shield drones with a Fire Warrior squad. Pad the squad to the full 12 man, take the Shas'Ui and give them a bonding knife. Deploy in hard cover and the WHOLE squad gets a 4+ Invuln save. Should the squad break then you have the better leadership and a chance at rallying. Only once have I ever had a squad that preferred to run for the back edge than turn and fight the enemy. Marauding Kroot took care of them after the game before they spread dissension in the ranks....

The humble Fire Warrior squad doesn't need shield drones. Save those points where they can be more useful. As for Crisis suits I personally prefer using only a Hq and his Bodyguard. I like the Stealth suits in my armies as they allow me the flexibility of deploying last and suddenly covering an apparent weak spot in my deployment.

Because the meta-game heavily favors mechanized army lists and fire warriors completely lack the ability to take special weapons (leaving them relatively incapable of dealing with vehicles). When a marine player spends 800 points on troops, they get meltaguns and/or missile launchers almost for free, or their choice of other specialized weaponry (but those two are by far the most common). If we spend 800 points on troops, we gain nothing in the way of dealing with tanks. Those marines also bring plenty in the ways of dealing with hordes (bolters do the job pretty much as well as fire warriors, as they are more accurate, which largely makes up for our higher strength, and there is also the frag missile to gain additional hits).

When fielding large amounts of fire warriors (or even kroot), how do you deal with the opponent that brings 10 rhinos/razorbacks? 15 chimeras? Lots of monstrous creatures? terminators? marines with feel no pain? You simply do not have the firepower to deal with these types of threats.

Let's take a look at a few of your examples, which you seem to deal with so easily with fire warriors:

Orks: Any green tide (horde orks on foot) will easily have 120+ models on the table, these models will also have at minimum a 5+ cover save (from the Kustom Force Field brought by at least one of their HQs) or a wall of walkers in front of them (killa kans) providing an even better 4+ cover save (for firing through a unit). That cover save means you need to inflict 33-50% more wounds on their units (upwards of 40 wounds for a full strength mob) in order to completely kill them, which you need to do because even a handful of orks can slaughter your lines of fire warriors in CC. You have at most three turns to do this before the tide closes the gap and engages you. Green tide orks also often have fast-moving distraction units, which buy the foot-slogging greenskins more time to get to you as you deal with those threats. And you can't ignore the distractions either, since they are locking your valuable shooting assets in close combat, which prevents you from firing.

Nidz: If they have swarms of infantry, then they have tervigons which reproduce those models each turn. Fire warriors have a difficult time killing MCs because they only wound on a 5+ and can't bypass their armor save. And that's ignoring their outflanking genestealers, deep striking mawlocs, or other monstrosities that are far more damaging than the little guys. Playing against nids is almost nothing like playing against orks.

Infantry based IG: Even if you play against one of these lists (which is one of the weaker IG lists by the way) Your fire warriors will be blown off the table by massed autocannon and heavy bolter fire, all of which wounds you on a 2+ and ignores your armor save. If you're in cover no problem, infantry-IG is more than capable of throwing way more wounds onto your frail fire warriors than you can pass with cover saves. Couple that with the fact that IG can straight up field more models in one troops choice than you can in almost your entire force organization chart, and you'll be hard pressed to weather that storm and still have enough firepower to do anything meaningful. Remember, you need to be outside of your devilfish (and therefore vulnerable to incoming fire) for at least a turn before you can make good use of that "superior" firing range, otherwise you're limited to the 12" rapid fire range.

Fire Warriors have very little going for them in Fifth Edition. They are overpriced and underpowered. If you're experiencing success with them than (and I mean no offense by this) you are facing players who simply do not understand how to properly build an army list.

one sec, why are fire warriors set aside automatically if your going up against a horde your not going to need anything specal in terms of equipment so they are relatively cheap, and if you equip them with pulse rifles, if you take out some of your elits, like stealth suits or maby cut back on the XV8, so not only can you keep laying down fire from the moment the game starts, once they get within rapid fire range they will be totally decimated.

Please take the time to write more effectively. Using correct spelling and grammar is essential to success at ATT and this post falls well below that standard.

Because fire warriors are more expensive than literally every other "horde" model in the game meaning you automatically get less than them (by a large margin). Kroot are much cheaper, bringing more shots to the table and more shots equals more kills equals less horde guys hitting your lines.

I've been looking over Imperial Armour Apocalypse 2, and found out about the XV9's Pulse Sub munition Rifle thing. Would that be good anti horde? From the looks of it, you can take two of it (Sadly I don't know if taking two twin links it or not, but since it doesn't say I'm assuming it doesn't Twin Link it.). Two pie plates of Gaunt shredding armour seems to be effective against Tyranids if you've got a few XV9s handy(Which is highly unlikely, but then again you could always try to convert, but that'll be a dosy...). That and you could also take the Phased Ion Gun which seems good, it seems to be a very shooty Bolter with better AP. Of course sadly, I won't be able to test these out due to my lack of funds and my friends' pure hatred anything Tau related.

So, Anti-hoard option would also be the submunition option to the railhead. This brings up an interesting conundrum I've been having. Can you fire both submunition and solid rounds in the same game?

i.e Hoards of 'Nids (Or other sufficient Hoard army like orks) is attacking. Use the solid rounds to take out the big thingy one turn, then use the submunition rounds to destroy hoardy thingy's the next?

Talking about XV9 I'd rather use the two twin-linked burst cannons with markerlight support to make BS better.

Hammerhead railgun shots have to be decided before each shot. It can shoot the submunition OR the solid shot each turn.

The problem I keep running into belongs to my Orky friend. He fields a 30boy squad with feel no pain and cybork bodies in games of around 1500 points. My issue is the combination of FNP and a huge unit with invuln saves leaves me at a loss for what to shoot at it. Should I try to pie plate it with the hammerhead? Ive tried using guns that ignore FNP but we don't have a lot of those and none of them have enough shots to dent that mob without pointing ALL my guns at it. Anyone got any ideas for this one? The rest of his force is pretty small for a green tide since he wanted them to be numerous AND hard to kill. The only other power players he has are his warboss and nobz, with similar FNP cybork stuff, and a large group of tankbustas.

You can kite the tank busters since they have to move toward the nearest enemy vehicle within sight so they are pretty easy to avoid.

If his warboss and nobz are on foot you can kite them also. Shut down that 30 boy squad and it will open up a lot of board space for your troops to move.

Also, always deploys as far forward as possible against Orks, then fall back shooting. This will keep your lethal weapons in range longer as opposed to waiting for the enemy to move into your range.

All good ideas. I'm gonna get another hammerhead soon to get another submunition shot per turn. deploying close to them is an interesting idea that I'm sure will confuse him a lot. I just hope I can stay outta his assault range while moving back. I know if I can kill that big mob his army will pretty much fall appart, I just wish we had a gun more suited to the job but I guess asking for a gun that has ap2 or better and has a huge fire rate is asking a bit much of any codex

We have plenty of options:

-AFP
-CIB
-5 shot crisis suits
-just about all our vehicles
-both types of troops
-markerlight support+any weapon in our arsenal.

Markerlights really are the bees knees when it comes to anti horde, more shots AND I ignore cover? Forcing pinning tests against Ld4? I'm liking it.

And now with tetras, we have a viable way of delivering them.