Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
After many games with Jax this is the build I find the most effective for his play style. To me he seems most useful in a 1v1 setting and this build does that. Except for a few games where I run into the overfed carry I can ruin almost any champ in a straight duel. There are only 2 that aren't nuke/mages I can think of at this moment that can give me a problem and that's Teemo and Xin. Teemo for the obvious blind and DOT, and Xin because he has a more consistent form of stun. Xin can be beaten, but only if you survive the initial burst combo and hes not running exhaust. You may feel that it's a giant hole in my build, but if you're not hitting you're just a meatbag. And always watch out for the mage/nuke, you have you're active ulti, but that may not be enough to save you from the massive combos that can come flying at you. Unless you initiate you're almost sure to die.
If you're looking for a different role for Jax I ask you to look into another build. I can participate in team fights by jumping to the back line and wrecking the DPS/carry of the other team, which is quite satisfying. If you're lucky enough to end up as the team carry enjoy the feeling when every champ on the other team runs in fear of Jax.
Right now my runes are fairly limited so I went with cooldown per level glyphs, dodge seals, and crit chance marks. I find that random crits are more intimidating than flat damage or armor pen. The other teams tend to forget about that 1 in 10 chance that you're going to hit for an enormous amount, this fact contributes to more than enough early kills when the other team overextends. It also helps in late game when you finally finish that Atma's Impaler. I'm going to experiment more with magic pen marks to see if it's a noticeable increase in my dps.
I start the game slow waiting until level 3 or 4 to try for a kill, unless the enemy champ does something silly and asks for the lamp in the face. This is because you have almost no harass options without putting your self in a bad place. Once you have 2 points in empower you really do hit like a truck. By this time, one of the opposing champs should be about half health, if you're lucky enough to get a good harass partner.
I know most people say to activate empower before you leap, but I find the 1-2 combo more effective. Early game it can be a toss-up on you're play style, but after 6 it gets you one hit closer to that relentless assault proc. Unless I know that they're going to run I try for the 1-2 combo over the empower/leap single hit. This also gives you time to take minion fire and hopefully proc that counterstrike, to prevent any fleeing that your victim may have had in mind. Ideally I don't leap until I have the proc active, but that's never 100% in the heat of the moment.
I've done my research and haven't found another build that's exactly like mine with the item choice. I prefer the hybrid aspect of the rageblade and gunblade. Most builds do include these but not as part of the core item set. Others tend to focus on early attack speed or forget that you're abilities benefit from BOTH AD and AP. I find attack speed unnecessary with both the rageblade and relentless assault.
I feel these are incredibly important to you're survivability in battle. If you're hitting you're healing and anybody who's ever played a melee dps knows that this drastically increases you're battle effectiveness. These items are so much more useful on Jax with his passive. I'm not going to argue with and extra 440 health on top of the other useful aspects of these items. Once you finish that bloodthirster you're arguably the tankyest DPS in the game. At level 16 with a full bloodthirster you can go and solo baron. Being credit to team battles without even being there.
I do appreciate criticism but be gentle and don't hate before you've tried it once. And yes that is my ingame alias.