It occurred me today that people are underestimating the amount of fire support needed to neutralize your opponent's vehicles. This is even more exaggerated when facing lists like mechanized Imperial Guard or any Razorspam list. Hell, I've even done it on occasion and it was evident when I ran scenarios in my head for a tweak to my Nova Open list. But how much is enough and when do you have too much? Unfortunately, there isn't a clear cut answer for this as there are other tactical means to marginalize vehicles, but knowing approximately where that sweet spot is becomes an important skill. Experience is the most important factor here, as you can only find out where that spot is by playing games in your "scene", whether it be on the local or national level.
Consider this: A typical mech IG list at 2000 points can contain anywhere from 15-25 meltaguns, 9-18 Lascannons, 6-9 Multi-Lasers, and 6-12 Autocannons. That isn't even counting ordnance fire. All mounted on 12-18 vehicles. How can you possibly think that a "typical" Black Templars list has enough shooting to deal with that? Its just not possible. Its why my gunline lists became so popular, so quickly. People realized that the traditional style of list simply did not have enough punch to compete. My earliest gunline lists featured between 28-32 Missile Launchers and Lascannons, plus a few plasma weapons and Autocannons. There was plenty of guns to blast that IG (or any army) list away, assuming average terrain.
However, even with those successes, I was a little heavy-handed in my approach initially. It didn't have enough support, namely in close combat, to sustain the shooting. Nor did it have quite as much mobility as I would have liked. And once everything was demeched, if you didn't have average rolling, cover saves would be the bane of anti-infantry shooting because there was not enough weaponry to torrent your opponent with. Flaws that could easily cost a Black Templars player games if they didn't know the lists and how to respond to these threats. Just like it took me all of Nova Open's Day One to re-adjust my play-style to account for the terrain we were playing with.
So where does this imaginary line find itself? We'll take a look at a MSU Space Wolf list this time. If using my Nova Open list from last year, each turn of shooting (using only 48" range weaponry) produces on average 4.568 Rhino deaths a turn. Way more shooting than we need. Of course, that is assuming no cover and the "infantry" passes their Righteous Zeal test. As we all know, Nova Open had so much cover that almost nothing went without a cover save, if you could even see the target at all. So if you pretend everything had cover, which was pretty common, then your number of Rhino kills per turn drops to 2.284. Not enough. Do that same thing on an IG list with twice as many vehicles (which also feature AV12, not AV11). You're going to be hard pressed to win.
Fortunately, as I mentioned earlier, there are other ways to deal with vehicles. You don't have to kill everything, especially if its not a vehicle. Often, stunlocking is sufficient. Refuse-flanking, reserves, mobility, and clever use of the threats in your list can also help localize your opponent's attention on small parts of your list at a time. Additionally, having cover can work both ways so it'll also be harder for them to kill you. MVBrandt defended the terrain his tournament used, but admitted there was perhaps too much line-of-sight blocking pieces on each board. Thus, we can safely assume that the terrain at Nova Open 2011 won't be the same as it will be at Nova Open 2012. However, its probably best to assume that there will be more than average. Adepticon this year also featured boards with pretty heavy amounts of terrain. So its not a trend that is going away.
Don't worry, I'm getting to my point. With boards using this much terrain, we can afford to take guns away and delegate them towards disruptive roles in our forces. Sacrificial units, close combat units, mid-field defenders, whatever you like best -- depending on the list. With so many choke points on a board, mobility plays a huge part in the game. The person who is able to take mid-field first, and hold it, will have a much easier time winning their game. The terrain also helps promote the survivability of close-combat units (and their transports) while they cross the board. You can afford to spend some points in this fashion, without hurting your list. The problem is, most lists people build now have taken too many guns out of their list and put too many of those points into dedicated close-combat units.
Even with a fully-chock board of terrain and cover as far as the eye can see, our close combat units are not efficient. The only unit that can make that argument are TH/SS terminators, simply because they are near impossible to kill even when walking. Everything else gets slaughtered in close combat against even the most basic troops of other armies. Grey Knights? They comprised 22% of the armies at a 256 player tournament (Adepticon 2012)! Their basic troops kill our most decked out Crusader squads in close combat without breaking a sweat, due to the built-in power weaponry. And those GK players that use Acolytes? They'll shoot you to death once they hit the 24" Psycannon range. Those lists also usually have Death Cult Assassins in them...and they eat MEQ for breakfast. Space Wolves don't inflict as much damage in close combat, but pound for pound, they are equals to the standard CC-oriented Crusader squad and will grind ours down to nothing at minimal cost to our opponent (and large cost to us). Blood Angels will do it even faster (and safer) due to Feel No Pain. Or if you're playing against a "Nipplewing" list, have fun cleaning up the dead Templars. Incubi? Wyches? Thunder Wolf Cavalry? TH/SS Terminators? Counsel-Seers? Too many things kill us in close combat without much effort or cost to our opponents. So small, inconsequential semi CC-units are best for us.
Going too far without guns is just as bad as having too many of them. In my experience, having 18-20 long range weapons (Str 8-9) in a 2000 point list should be sufficient for most lists. This is provided you also include melta in your list, as well as some form of CC-support. In some of my recent lists, I went under this mark and it became noticeable in my games against mech IG. I was better equipped for foot/horde lists, but if I saw too many vehicles, I had trouble. Obviously, as mechanized armies are much better, these deficiencies were a problem. As Nikephoros frequently mentions, playing your lists against a gauntlet of armies is incredibly important to find the stress points. It'll help you find out where you can sacrifice things, to bolster other elements of your force, without screwing you over. Likewise, you should start to discover anything in your actual gameplay that is causing you to lose games (i.e. tactical choices, target priority, decision making in general) and give you the chance to address those issues before any important games. In my case, I had dropped a little too much fire support from my original gunline list and it hurt my ability against mech IG...an incredibly common opponent on the USA GT scene. Thus, I had to address that problem if I wanted to succeed.
I challenge you to go into your "scene" and play around with your lists a bit. Take some guns out and see how you do against highly mechanized lists. Likewise, put lots into your list and play the same game. Find the middle-ground, where you are comfortable with how your shooting played out with average dice rolling. Then play against another opponent who runs a totally different style of army and see how you do. Obviously, if you're not competitive, this doesn't matter. But if you are, you need to find out how much fire support you can get away with safely. The dice won't always favor you, so if you're unsure, it doesn't hurt to overcompensate by having more AT. Games aren't lost on turn one by having too much AT, but it certainly could be if you don't have enough.
So did I give anyone a clear cut answer as to how much AT shooting is enough? Of course not. That isn't how I do things. And even if I did, what might be enough for me and how I play games, may not be enough or too much for the next person where they play. I can only give you an estimate based on my own GT experiences. Nevertheless, hopefully this article was useful in helping people to understand why finding that sweet spot is so important. Understanding the proper amount of AT firepower in competitive list building is the single-easiest way to improving your W/L record. I can't do it for you, so get out there and play some games!