Gunlance Overview

Gunlances (ガンランス Ganransu), also known as GL, are long, piercing weapons with a mechanism inside which can fire an explosive round. This is called Shelling. Unlike Bowguns, the Gunlance cannot fire over distances. The Shelling ability can only be used from close range and reduces the weapon's sharpness with each use. The use of the weapon is largely similar to the original Lance. Unlike ranged weapons, Gunlances come with preset, unlimited ammo. They are able to charge up, indicated by the radiating energy at the tip of the lance, and dish out a strong explosive attack referred to as Wyvern's Fire. 

- Weapon Traits :

• The Gunlance has piercing damage, meaning it has a bonus damage for every piercing attack you do, and most of the monsters in the game are very weak to this kind of damage. It could be said that the damage goes almost directly through a monster. Meaning that while most weapons will have a damage reduction due to the monsters defense, a Gunlance user (as well as a Lance user) will have most of their base damage go unaffected.
• The Gunlance provides the hunter with Shielding capability which is as good as a Lance user due to the size of the shields. Lances and Gunlances have the strongest Shielding capability and can block some attacks that other shielding weapons would otherwise find unblock-able.
• The Gunlance has the Quick Draw feature, allowing the hunter to quick draw the weapon to shielding position just by pressing "R" button and then triangle while standing still, which can be very useful.

• The Gunlance has the Shelling Ability. As the name implies, the lance has a gun embedded in it, which will activate with a press of a button. The best way to think about it is a regular lance with shaped charges strapped to the end. The shots are quite short ranged, but work well when linked with the stabs of the Lance. You can see the amount of shells you have remaining on the upper left side of the screen and you can reload by pressing circle while defending with the R button, or by pressing "O" after a back jump. 

• • The type of shells fired differ depending on the individual Gunlance. These usually range from Level 1 to Level 3 shelling (though some go as high as Level 5, Monster Hunter Frontier currently has Level 6 Gunlances), and come in three different types: Normal, Spread, and Long. As the names imply, each type works differently.

  • Compared to a [Normal] type Gunlance, a [Spread] type's Wyvern Fire will have a wider blast radius, while a [Long] type is granted greater range. Regardless of level, a [Normal] Gunlance has 5 shots, [Long] types have 3, and [Spread] types have 2. However, [Long] and [Spread] shots inflict more damage than [Normal] shots

  • The shelling feature has a downside: it burns through the weapon's sharpness. Using it will quickly dull the weapon. Whetstones are strongly recommended when using this weapon.

• Gunlances come with an incredible explosion attack known as Wyvern Fire. This attack can be done by pressing the circle and triangle buttons while defending with the R button. The delay is usually 3 seconds and you have to be close for the attack to land. The downside is that after using it you'll have to wait for your weapon to cool down before being able to use Wyvern Fire again. The cool down period is 110 seconds. Also the Gunlance's sharpness will dull after use (similar to Shelling) and leave you vulnerable to attack shortly after use. Wyvern's Fire is four times the length and four times the damage of its shell shot. It is one long blast that is divided into four sections, so if you hit a wyvern very close up you would do the full four times the damage, but if you hit it at half the length, you only do twice the damage of shell shot and so-on.

• The Gunlances, just like the Lances, can chain attacks. An example would be an attack from 3 single forward stabs to a shelling shot and repeat, or mix up with an uppercut (circle plus triangle) to diagonal attacks. See the video below for a great tutorial on how to do these combos.
• The Gunlance also has a new attack where if you hold down the shelling button you can charge up any single shell shot.

- Generation Changes

Monster Hunter Portable 3rd

The Gunlance received a large boost to its moveset in MHP3, making it a more aggressive weapon in the game.

• Gunlances in MHP3 can now do a Quick Reload, which reloads a single shell at high speed with the opportunity to fire a slightly delayed shot afterwards; this shot in turn can be chained into another Quick Reload for an easy infinite combo. This can be done by pressing after every shot.
• The Full Burst is a new attack for the Gunlance. This occurs in certain combos, most commonly by pressing the button three times. The weapon slams downward to the ground after the third press of the button and fires all the current number of shells the Gunlance holds, creating a massive explosion that greatly damages all foes within its radius.

• In addition, the forward stab can be linked into a downward smashing attack; the smash can then be chained into a Wyvern's Fire attack or to a Full Burst.

• Charged Shelling is also a new attack for the Gunlance, where it charges its shells first before firing at the intended target. This can be done in a number of ways; one of them is by holding the button and pressing the at the same time.

Monster Hunter 3 G

• Removal of the auto-guard glitch present in Portable 3rd.

Monster Hunter 4

• The Gunlance can now do a slam attack after jumping off a ledge and do a Full burst or Wyvern's Fire after jumping.
• The Gunlance gains a new attack pressing R+A when moving forward. The hunter makes a small Dash forward and fires a shell. If the hunter makes this move near a ledge, it will shoot a shell in mid-air.
• The Gunlance can do the Wyvern's Fire while jumping.

Monster Hunter X

• Tha Gunlance now features a "Heat" gauge, whenever the weapon's user fires a shell, the bar start filling up. When the gauge hits a level (yellow, orange, red), the damage of the Gunlance's attack (not shells) increases. However, when the gauge hits the limit or using Wyvern's Fire , the Gunlance becomes "overheated" and can't shell for a period of time . The heat bar's level is reduced by evading or not shelling for a while.

• Also, when the Wyvern's fire is used, the heat gauge slightly depletes after going on overheat.

- Pros and Cons :

Advantages

• Consistent and reliable shelling damage with its fixed and unblockable damage.
• Capable of executing a variety of relatively fluid combos by mixing up stabs and shelling.
• Versatile range and attack direction, able to attack at 45 degree and 90 degree angles (overhead). Coupled with Long shell types, the Gunlance becomes one of the longest-reaching Blademaster weapons.

Disadvantages

• Shelling, and its associated special attacks, chew through sharpness relatively quickly.
• Gunlances cannot fire shells when sharpness is at red level.
• Heavy settle animations on most actions (Reloading, lance slam, Full Blast, Wyvern Fire etc.) that leave the user open to attacks.
• Only method of dodge is a single backhop/sidestep with very short invincibility frames, giving Gunlance users limited evasive options.
• The Gunlance's wide spread shelling attacks (Wide shells, Full Blast and Wyvern Fire) pose the large risk of friendly fire disrupting nearby hunters.  

- Tutorial for Beginner Hunter (by GaijinHunter)
https://www.youtube.com/watch?v=PcOKIvrWUL0