Building Mechs (Intermediary)

There are many mechs you will encounter in MWO. For the most part, they can be categorized by the ranges of their weapons, and subdivisions appear beyond that. The three ranges are short, medium, and long. Of the three, long and short are by far the most popular. You see a number of builds using mixed-range weapons, but in general there is a single range at which all, or almost all, of the weapons in such a build are effective, and that is the range that the build focuses on. This is because the main challenge of the game is less to shoot the enemy than it is to dictate the terms of the engagement, which includes how far away the enemy is when you are shooting at each other. If you are successful at the latter, you will only be engaging the enemy at one range, and if you are unsuccessful, you will be playing your opponent’s game at a disadvantage. However, how to dictate the terms of engagement is beyond the scope of this piece; what we care about for the moment is that a good build will try to only engage the enemy at a single range.


There are a number of short-range weapons in the game (which we will define by having an effective range of 300 meters or less, with a few exceptions). These include the AC/20, SRMs, and Medium Lasers. However, other weapons that are effective at longer ranges are commonly used on short-range mechs, including weapons like the Ultra AC/5. The main types of short-range mechs are scouts, brawlers, and harassers.


As far as medium-range weapons go, we will classify them as having an effective range between 300 and 700 meters. Weapons that fit this description include the AC/10, Large Laser, and the UAC/5. Due to the flexibility of this range, most mechs that focus on engaging at a medium range will have other weapons that are otherwise characterized as short- or long-range weapons (though usually long). Medium-range weapons are not ones that you can use to snipe across the map, but you can engage short-range mechs without risk as they approach and out-DPS most long-range mechs while within your optimal range. The most common types of mechs at this range are firing line mechs, but you will also find some all-purpose mechs that will use this range to do their business.


Long-range weapons include all of those which are most effective over 700 meters. This includes weapons like the ER Large Laser, Gauss Rifle, and LRMs. At this range most mechs will be fire support, either direct or indirect. It is also fairly common for a long-range mech to carry backup short- or medium-range weapons to help deal with an enemy that gets too close for comfort.

Support Weapons:

This is pretty self-explanatory, and at the moment the only “weapons” that fall in this category are TAG, NARC, and AMS. These do not do damage directly, but they are useful to increase the damage dealt by your team or decrease the damage dealt by the enemy team.


There are really only three resources I use to build a mech: Smurfy’s Mechlabmy own spreadsheet that I cooked up to keep track of optimal engine sizes, and Snafet’s website which lists out IS mech quirks. Now, the spreadsheet is hardly a definitive list because it does not take into account things like hardpoints or critical slots, but i like to keep my engines close to the guidelines if I can help it. I use Smurfy’s because it is straightforward and the closest facsimile to the in-game mechlab I know of, and it also provides a lot of important information at all times (such as open critical slots). Other than these, I rely mainly on my experience to make a good mech. For a good showcasing of how I build mechs, I recommend checking out the stream I did where I made a build for every IS mech.

How to test a mech’s worth:

There are many ways to try to determine if a build works. You can look at the firepower, heat efficiency, weapon ranges, etc. But the only way to definitively test a build is to take it into battle. That is not to say that having one good game with it makes it a good build, or that one bad game with it makes it a bad build. Testing it repeatedly in multiple scenarios is the only way to inform yourself with an honest opinion on the merit of the build.

However, there are ways to at least gather information on whether a build can be improved before a live-fire environment. After creating a build of your own, I would recommend going through this process until it becomes second nature:

Do I have open slots?

Depending on how many open critical slots you have, you can do a number of things. If you have 14 or more critical slots empty and are lacking either Endo or Ferro, get them (Endo is always better than Ferro if you can only manage to fit one). If you add Ferro, remember to adjust your armor so that it brings you to a round tonnage value (.5 or .0).

Can I build this more efficiently on a heavier/lighter chassis?

A good example of this is comparing the AC/20 Blackjack to the AC/20 Yen-Lo-Wang. Using identical weapons and considering either a standard or XL engine show that the Yen-Lo-Wang is just better at the build (Standard Engine Yen-Lo-WangStandard Engine BlackjackXL Engine Yen-Lo-WangXL Engine Blackjack). This also goes the other way around; many times a Jenner is a better pick than a Cicada if you are going for the max engine size, and this is where the engine efficiency sheet comes into play. If you have two mechs with similar hardpoints but different tonnage that you are considering for a similar build, you can look it up on the spreadsheet to see which you can get closer to the target engine size, and go from there.

Are my weapons appropriate?

Are you running a hardcore brawler build with an LRM 20 or a PPC? A sniper build with an AC/20? Remember, you want there to be a specific range that all of your weapons work well at. Just because your LB-10X can hit at up to 1620 meters does not mean you should be using it from anywhere near that far away.

Are there any utility items I can fit that I might need?

Using streaks without ECM or BAP? You might want to rethink that. And sometimes it can be good to pack on that AMS or Tag to help your team (and yourself) out. This much is ultimately up to your taste and what role you expect your mech to fill so there is no definitive right or wrong, but try to make sure you are not forgetting about anything that could help you out of a jam.

Do I have enough/too much ammo?

Eventually you will figure out how much ammo works for you for each ballistic or missile weapon, but if you have used a build for a while without ever running out of ammo, it is time to take a ton out (unless there is only one ton total, of course). And if you are running out more than, say, 25% of the time, it is worth considering adding a ton.

Where is my ammo?

All ammo that is not gauss ammo can explode. The key is to put your ammo where it is least likely to get hit, or where its explosion causes the least trouble. The components that will generally be exposed the least often are your legs and your head. Everything else will get shot to shit more often than not, but the furthest away you can get from your engine is your arms, and that is where we will put the remaining ammo. On a related note, do your best to keep a gauss rifle explosion from coring you out. That means that you want to fill up as many critical slots in its component as you can (dynamic armor/structure slots do not count) so that the chances of an enemy critical hitting one of the slots the gauss rifle is in are lowered. I also highly recommend throwing in some CASE when it is in a side torso with a standard engine.

(For Inner Sphere mechs) Could I use an XL?

This is less about whether you could fit it into the slots than it is about how well the mech would use it. An XL is a risk, but it can pay off big time if you do it right. The two main things to consider are how fast it will make you go, and how vulnerable your side torsos are. Obviously (although I see it happen way too often – and not just on trial AS7-K’s), using an XL on an Atlas is just a no-no. You will lose at least one side torso before your center torso more often than not, and the fastest you can move is less than 65 after speed tweak. The opposite extreme of this is on a Jenner; the perfect example of what to use an XL on. The center torso is huge, the side torsos are not, and using an XL will either save you 9.5 tons (more than a third of the mech’s total weight) or give you an extra 40 KPH. A less extreme example of this would be the Cataphract, in which good arguments can be made for and against XL use. The side torsos are not small, but they are not always priority targets either. The speed gains and weight savings are considerable, but they are not extreme. A case like this is ultimately situational. If you are going to be in the middle of the fight, a standard is usually your best bet. But if you are sniping or harassing, you can usually afford to fit an XL. It is a judgment call in the end, and that judgment develops over time.

(For Inner Sphere mechs) Am I taking advantage of the quirks on this mech, or is this build better than one that would take better than the quirks?

This is a difficult question to answer for yourself, and it is one that I have struggled with on several occasions. Quirks are great (you can find a full list of them on Snafet’s website) and sometimes it can be tempting to take a sub-optimal build just because the quirks on it are so good. But if you directly compare that build to another one that you made without considering quirks and the quirked build comes up short, it’s simply not optimal. However, maybe it can lend you an insight on a way to improve the other build which might take some slight advantage of the quirks (such as replacing an AC/5 with a UAC/5).

(For Inner Sphere mechs) Do I have double heat sinks?

If the answer to this question is no, put in double heat sinks. Trust me…


After you get all of that out of the way, take her into battle and just see how she feels. If you are looking for help with a build, feel free to post it over in the Build Emergency Room in the MetaMech forum.