Hello, and Welcome to the Gun Specialization Guide.
In this thread, you'll learn about how to use guns effectively for Normal Mode and Hard Mode Subsequently. 
Getting your first gun:
When starting off in a new world, you'll most likely not find anything that amounts to a gun quite yet.
The closest Ranged gun-like weapon you'll most likely find first is the Blowpipe.
This is an easy to use weapon, as grass can be cut for seeds, which is your ammunition for the blowpipe.
As soon as you have access to a Demolitionist, you'll be ready to obtain your first REAL gun.
head to the nearest corruption or crimson and delve into the catacombs below with Bombs or Dynamite.
The golden orbs can be destroyed with a chance to obtain the Musket.
The Musket's high damage early in the game, along with its slow fire rate, help to conserve ammo, and it can be used to effectively kill the various eaters in the Corruption. Its best modifier is Unreal.
If you're in the Crimson, the Undertaker will replace this gun from destroying the crimson hearts.
As it has no knockback The Undertaker cannot acquire the Unreal prefix. Its best prefix is Demonic for Damage and Critical Chance, and Rapid for Speed and Velocity.
You'll now be using a new type of ammunition as well, called Musket balls. Be careful not to run out of these for now.
Any Movement Increasing accessories are preferred as well.
Finding Better guns in Pre-Hardmode:
Once you've gotten a gun, there's a good chance a Gun Dealer will show up.
He's got some pretty good stuff, and will be your best friend for ammunition throughout the game.
As soon as you can, make sure to buy yourself the Flintlock Pistol at the price of 5 gold for it's faster attack speed, unless you got the Undertaker.
The best modifier for a ranged weapon with no knockback is Demonic.
If you're lucky and you have him during the Blood Moon, make sure to purchase his more powerful Silver Bullets for the 2 extra damage and higher knockback.
The Minishark may be fast- but it's very costly. At this point, you probably won't have the 35 gold to purchase it and subsequently, the large amount of bullets needed to feed it. So unless you're rich/had a wealthy donation, don't buy this weapon.
From this point on you'll be wanting to obtain 2 other ranged weapons before going into hardmode.
If you're searching around the Jungle, you may find a Boomstick in the jungle shines.
The best possible modifier for the Boomstick is Unreal, and the gun shoots a spread of 3 bullets while only consuming one.
If you've killed Skeletron, then you'll want to find the Handgun within the chests of the dungeon.
Its best Modifier is Unreal.
Once you have that handgun, you'll need 10 Hellstone bars, which can be found by mining Hell.
With that, you can transform your handgun into the best pre-hardmode gun found, the Pheonix Blaster.
Its best Modifier is Unreal.
You'll also be wanting to make new bullets for yourself now, called "Meteor Shots"
These bullets can bounce from any surface once or penetrate up to one enemy. It's damage is the same as silver bullets, although the bouncing ability is useful.
Early Hardmode Guns:
As soon as you kill the Wall of Flesh, you'll most likely find a Clockwork Assault Rifle.
(if you also find a ranger emblem, equip it.)
The Clockwork Assault Rifle is a gun that fires in three-round bursts. It is sometimes dropped by the Wall of Flesh. Only the first shot out of the three will consume ammunition. The attack button can be held for repeat fire.
This weapon's high rate of fire and low ammo consumption make it ideal for mowing down large packs of enemies. This is useful during invasions, especially if the invaders can be grouped up in chokepoints. The best modifier it can receive is demonic.
Your Gun Dealer will also now sell the Shotgun and Empty Bullets.
If you have enough money, go ahead and buy the shotgun, but disregard the Empty Bullets.
The Shotgun fires a 4 bullet spread, which is an upgrade from the boomstick and has higher damage.
Its best modifier is Unreal.
The Traveling Merchant will also now sell the Gatligator for 35 gold.
This is a good buy, as it is a powerful rapid-fire weapon with a 50% chance not to consume ammo.
The only downside is that it has terrible aim.
You'll be wanting to also start on crafting wings of some sort, and gaining better accessories.
Hardmode Late Game Guns (The Best of the Best):
There are 5 guns that you'll want, now that you're at the top of your game.
It is required that Plantera and Santa NK-1 can be defeated at this point- this is how you'll get these guns.
The Tactical Shotgun is a Hardmode, post-Plantera auto-fire weapon. It is an upgraded version of the Shotgun, auto-firing six spread shots per bullet consumed.
It is dropped by Tactical Skeletons in the Dungeon, only after Plantera has been defeated.
Its best possible Modifier is Unreal. The Ruthless Modifier will alternatively add an exceptional 18% damage, at the cost of 10% knockback.
The Chain Gun is a Hardmode, post-Plantera gun. It has a 50% chance of not consuming Ammunition, but fires in random directions over a wide spread. It is dropped randomly by Santa-NK1 during the Frost Moon Event.
Its best Modifier is Godly or Rapid.
It also has a use time of 4, which is the fastest of any weapon in the game.
The Proximity Mine Launcher shoots mines that explode when a player/mob steps within range of radius and can be bought from the Cyborg NPC. The mines are heavily affected by gravity and will only travel a short distance before dropping to the ground. After hitting the ground, these mines will not roll if they are on a flat surface and will 'stick' to the ground. Shortly after it stops moving, the mine will turn semi-invisible.
The mine will also explode after a few seconds if nothing steps on it. In that time if the player is within its explosion radius the player will also be damaged. Care must also be taken by the player to make sure they are not in the effective radius of their own minefields when enemies trigger them, because enemy-triggered explosions will still harm the player and being caught in a field of them can quickly drop a large portion of the player's health.
The best Modifier for this weapon is Unreal.
This gun uses rockets instead of bullets, which can be bought from the Cyborg as well. you can obtain the best rockets, which are Rocket IV's during the solar Eclipse.
The Snowman Cannon is an upgraded version of the Rocket Launcher. It has a chance to be dropped by the Ice Queen during the Frost Moom event. It fires Rockets which home in on nearby targets and explode on contact. The rockets fired are re-skinned miniature snowmen. Unlike most rocket launchers, the splash damage of rockets fired do not harm the player. Also unlike the Rocket Launcher, it can obtain the Unreal Modifier.
Lastly, the Holy-man of all guns, the most DAMAGING of all guns, behold, you'll want the:
Sniper Rifle is a Hardmode post-Plantera Weapon that fires a bullet with extremely high damage, though at a far slower rate of fire than most ranged weapons, and has a "zoom" feature. It cannot be auto-fired. The Sniper Rifle is uncommonly dropped by Skeleton Snipers in the Dungeon After Plantera has been defeated.
The Rifle's zoom capability is identical to the Rifle Scope and the Binoculars' abilities, whereby the screen scrolls temporarily in the direction of the mouse cursor while holding the right-click button, essentially extending your viewing range in one direction.
The Sniper Rifle has a base 19% critical strike chance as opposed to the usual 4%.
Its best possible Modifer is Unreal, but to obtain the highest damage it can possibly do, the best modifier is Ruthless which, with all other accessories included, gives you 334 damage while not moving. 
(why not the Coin Gun? Because it's way too expensive.) 
What about the Bullets?:
One word:
Chlorophyte.
Many people think that you'd want the Venom bullet, as it has a higher damage.
Chlorophyte Bullets are late-game Bullets with homing capability.
While expensive to craft due to the Chlorophyte in their recipe, and having an average base damage (10), this is offset by their strong homing ability. Bullets can turn sharply and even curve instantly around to hit enemies behind the player. Chlorophyte Bullets are ideal when precision is required: Just aim in the general direction of your target and the bullets will take care of the rest.
These bullets are fairly efficient, as few will be wasted (by missing) in most conditions. However, caution should be used in tight or enclosed areas: the bullets will home through solid blocks, wasting shots if an enemy is on the other side. Shots will also home in on the closest target first. If a target is killed while a bullet is tracking it, the shot will continue in a straight line like a normal bullet. Chlorophyte Bullets will not switch targets even if they are within homing range. Also note that the bullets, while having a fairly tight/small turning radius, require a reasonable amount of clearance for U-turns. Insufficient clearance will result in them hitting blocks and being wasted.
Chlorophyte Bullets pair well with guns that compromise on accuracy in favor of a high fire rate or wide spread, and/or a chance to not consume ammunition, eg. the tactical shotgun and Chaingun. The homing effect negates the spread, and low ammo consumption lowers the expense of keeping this ammunition stocked.
Armor Specialization:
At this point in the game, you'll also be crafting special armor that gives bonuses to particular weapons or items.
For a Gunman, your best armor option is to craft Shroomite Armor with the Shroomite Mask being your Helmet of Choice.
Shroomite Armor is an endgame Hardmode armor set that boosts the effectiveness of ranged weapons. It also features a "stealth" effect that turns the player partially invisible, and further boosts weapons, when the player stands still. This only works when the armor is equipped, and will not work if armor is in vanity.
With a full set equipped, standing still causes a player to enter stealth mode, and over the course of roughly 1.5 seconds, the player will go from partial to near-full invisibility, which also diminishes the chance that enemies will target the player. Additionally, during this time, weapon damage, critical strike chance, and knockback will each be boosted gradually up to maximums of +45% damage and +10% critical chance at full stealth. These boosts increase both weapon and ammo damage. The buff begins fading quickly with movement, but is not immediately dispelled.
Shroomite armor has three headwear options, each providing an extra +15% damage boost that affects a different ranged weapon type, the Mask being the one needed for the damage boost for any gun that uses bullets.
Crafting Shroomite Armor requires Shroomite Bars (crafted from Chlorophyte bars via the Autohammer, which is in turn purchased from Truffle). Crafting a full set with a single helmet requires 54 Shroomite Bars (or 810 Glowing Mushrooms and 324 Chlorophyte Ore).
Gunman Accessories:
There are 5 things a ranger needs as well, in order to ensure maximum mobility, damage output, and other bonuses.
The Ankh Shield provides immunity to 10 different debuffs, gives knockback immunity, and provides an additional 4 defense.
The Lava Waders allow the player to walk on water and Lava indefinitely. They also offer immunity to fire blocks, and allow the player to enter Lava for 7 seconds. The seven-second countdown only applies when within Lava; standing on Lava can be done indefinitely.
The Ranger Emblem increases ranged damage by 15%. It is occasionally dropped by the Wall of Flesh.
Fishron Wings allow you to fly and give these bonuses:
- Unhindered movement in liquids.
- 25% extra ascent speed.
- Bubbles during use, not lit.
The Celestial Stone is crafted from a Sun Stone and Moon Stone at the Tinkerer's Workshop. It offers the same boosts as its components do, and as such, it is active during both Day and Night.
Stat bonuses are listed below:
- +10% melee speed
- +10% damage
- +2% critical strike chance
- +2 HP/s life regeneration
- +4 defense
- +15% pickaxe speed
- +50% minion knockback
Backup Items, Potions and Minions:
The best Gunman also carries a few other things to suppliment his/her arsenal.
The Possessed Hatchet makes for a quick, short range melee weapon (although it looks like a ranged item) that can protect you from tight-range skirmishes.
Minions such as the Pygmy Staff, Raven Staff, Tempest Staff and Staff of the Frost Hydra are perfect for backup in most situations. I prefer to use the Frost Hydra Staff as it provides excellent cover.
for Potions, I recommend using the Ammo Reservation Potion, Ironskin Potion, NightOwl Potion, Rage Potion, Swiftness Potion and Wrath Potion for whatever situation you might find yourself in.
Ammo Boxes are extremely useful as well- Placing them in strategic locations will enable you to have a 20% not to consume ammo buff for when you need it.
A Web Slinger should be your grappling hook of choice, as it gives you a larger manuvering range.
Carrying a few forms of magic, such as Magnet Sphere or Razorblade Typhoon will ensure you've got a 3 way of attacking.
Also make sure to have a Wisp in a Bottle for increased vision underground or up top.
How Do I Play as a Gunman?:
To use your guns effectively, you should always keep a distance from your enemies. That's what your wings are for. Always keep moving and be far away from them.
In any fight situation, you should let your guns do the work for you, as they'll be producing the damage so you can focus on dodging.
The biggest difficulty to being a gunman is your ammo upkeep- even with multiple buffs, you'll run out pretty quickly with things like the chaingun. So make sure your bullets are always stocked.
if you do run out of bullets, make sure you've got your magic and Melee backups on-hand. This can mean the difference between life and death.
Also, never be afraid to retreat for a second or two to regain health, or to re-buff. Chances are that you're going to easily be able to get away from whatever is chasing you- enough to heal or get back on your feet.
Thanks for reading my Gunner's Guide.
If I forgot something, please PM me about it.
Happy Shooting!
