Fortunately MH4U is extremely gunner friendly and anyone who's thought about gunning in the past should really give it a shot (pun very much intended). The introduction of item sets has made it incredibly easy to manage multiple gun types and it makes it much quicker to switch from blademaster to gunner on the fly so it's no wonder why a lot of people are looking to make the switch and if your still not using item sets yet then it's time to get your head out of the sand.
Perhaps the best advise is to approach gunning like a traditional RPG, let the monster perform and attack and then when it's your turn, you attack, and so forth. Having low defense means you have to be extremely careful especially at end game, many 140 monsters are capable of one shoting gunners so if your just starting out make a defensive set that you can swap pieces out of as you start to get more comfortable.
- Be mindful of your surroundings. Rolling into an invisible wall or piece of scenery can get you killed, so don't be afraid to sacrifice damage for positioning and be mindful of whats around you.
- You also want to make sure your not baiting monster attacks that can cause them to end up in an unfavorable position for your team; lava pits, walls that can't be scaled, varied elevation, etc. Which leads nicely into the next tip...
- Be aware of your positioning relative to monster AI. Knowing what ranges a monster will perform a specific attack can be very helpful to both you and your team, most monsters ranged attacks are easy to avoid and give fellow blademasters a great opening, conversely standing too close might prompt a charge attack, which causes blademasters to lose positioning and can be harder to avoid.
- Maintain critical distance. Critical distance grants a 1.5x damage multiplier so it's extremely important to always make sure every one of your shots has that sweet sweet screen shake on it (this doesn't apply to elemental shots).
- Know your weak spots. Guns get their extra punch from being able to consistently hit the weakest parts of a monster, this is true for all weapon types but it's especially important for guns.
- Ledges. Air attacks grant you a reload and aren't particularly useful for mounting. You can also put your weapon away as you fall down a ledge to quick put it away, very useful for HBG's.
- Use items. Traps and flashes work out particularly well for gunners, especially considering you can just set up shop behind a pitfall or shock trap and safely shoot with out worrying about a deadly charge attack, just be careful when laying traps.
- Eat for Moxie. This is up and away the best kitchen skill for new gunners starting out at end game. Don't under value this skill, it will save your life frequently when starting out.
Crafting your Set:
- Know your gun. Try to plan your set around a particular gun. Aim to use a specific ammo type and try to make the most out of it with your given skills. Skills like stead hand may sound great but you'll most likely be relying on one or two shot types exclusively for the bulk of your damage.
- Ammo. You can classify ammo by 3 categories: Ammo that can be bought and is easy to make, ammo that can be bought but not easily made, and ammo that can't be bought or easily made. Always look up the combine materials and how to get them before investing time into crafting a new weapon and set, don't make the mistake of crafting a weapon that uses an ammo type that is difficult to obtain and expect to use it regularly. You also want to make sure you can carry plenty of a particular ammo type, you don't want to center your damage around an ammo type that you might not get a lot of.
- Helms are interchangeable between blademasters and gunners. An extra 60 defense can stop some monsters from being able to one shot you so if you can, try to find a set that works with a blademaster helm.
- Balancing defensive skills vs offensive skills. Some fights are going to be harder than others, know when to use what skills and plan to make modifications to your set as you get more comfortable with gunning, safety is paramount when starting out, plan accordingly.
- Take advantage of combine skills. Prudence/Fleet Feet and Brutality work out particularly well for gunners. Perhaps you have a good piece of relic equipment, try to incorporate it into your set if you can. Stay away from steady hand however, most of the time you'll be sticking to one type of ammo so it's not particularly useful and difficult to put on your sets.
Gun Specific Skills:
- Recoil Down. Recoil works as a threshold depending on your gun's recoil and shot type. If your recoil is too high it greatly reduces the speed at which you can use a particular shot but so long as your under the cap having a higher recoil won't make you shoot any faster. For pierce shot a gun with some recoil won't need any reduction, average recoil will need recoil down +1, high recoil will need recoil down +2 (again this only applies to pierce shot it's going to be different depending on the bullet your using). Before making a set make sure you test your gun's recoil and ammo type in the field to find out exactly how much recoil down your going to need.
- Normal/Pierce/Pellet Up: Adds 10% more damage to the given shot type. Very useful and a lot of extra damage for just 10 points.
- Bonus Shot: Great skill for LBGers. If your rapid firing normal or pierce it's not as useful as it's more intended to make the most out of bullets that have a limited carry amount. Great for Crag/Clust, status, and Element LBG's.
- Reload Speed: Not as important as you might think, your mostly going to use a gun that has plenty of bullets of the given shot type you want to use, also the jump reload also helps minimize the need for this skill. If you can only load less than 3-4 of the bullet your using at a time I'd consider this skill, anything more than that and the benefits won't be as apparent.
- Load Up: Having an extra bullet in the chamber adds some extra damage. This skill is particularly useful when using the bow or status/crag/clust shot.
- Trajectory: This is a great skill for new gunners and most players highly recommend it. Shooting outside critical distance is where a lot of newer gunners lose their damage and moving in close can be very risky, chances are if your reading this guide your going to benefit from this skill. This skill will help you out both offensively and defensively as it'll help you maximize damage while keeping you safe. Very under rated in my opinion, it's also pretty easy to gem on. Bow users would be wise to use this skill as using a bow with out dash juices is considerably unsafe and that extra distance can give you just enough time to recover stamina for an evade.
- Evade Extender: This gets first mention, if your a new gunner plan to use it. It'll keep you safe and help you get into position faster, potentially increasing your damage output.
- Evade: Some LBGers swear by it, personally I think the positional benefits of evade extender give it a better balance between defense and offense but there are a handful of fights where evade will keep you safer than evade extender and vice versa.
- Divine protection: Not a bad skill for gunners, if you eat for felyne defender this skills is even more helpful, unfortunately it doesn't offer much of a combat bonus the way evade extender and evade do outside of helping you stay alive so only use it if you really feel it's necessary. Guts. If your really worried about getting one shoted you may want to consider bringing this skill along.
- Fire/Thunder/Ice/Water/Dragon Attack: The elemental attack skills work very well for LBGers who want to rapid fire elemental shot, this can make elemental rapid fire LBG gunners quite powerful. Challenger: As a gunner it's easy to keep up damage when a monster is frenzied so this skill can go a long way.
- Peak Performance: It's easy and recommended to stay at full health and grants you an attack up (L) bonus. Very nice.
- Weakness Exploit: As a gunner you have more openings to hit the targets you want so a skill like weakness exploit is particularly handy at picking up extra damage.
- Attack up: Obvious reasons.
- Expert: Every little bit helps.
Skills that sound useful but aren't:
- Precision. Generally deviation isn't going to be that much an issue unless your shooting out of critical distance, which you should never be doing. Also if you've gunned in older monster hunter titles you'll notice that deviation is a lot less harsh this time around.
- Combo Rate. This skill can help out but generally you'll be relying on no more than 3 shot types so don't worry about this too much, just bring combo books.
- Steady hand. Generally you want to stick to one shot type. So avoid this skill as it's not worth the points it takes to put this on your set.
Credits: Special thanks to ken_jammin for the tip and guide.