The XO16A2 Chaingun (Presumably the full name being the XOTBR-16A2 Chaingun) is a Titan weapon appearing in Titanfall 2's singleplayer campaign, wielded by Vanguard-class Titans such as BT-7274, as well as the game's multiplayer, wielded by Monarch-Class Titan that was implemented through DLC. It is manufactured by Brockhaurd Manufacturing, and is the presumed successor to the XOTBR-16 Chaingun.
The XO16A2 performs very similarly to its predecessor in the first game. It is available on the Expedition loadout in the campaign for Titanfall 2, and on the Monarch in multiplayer.
The XO16A2 is the weapon used in the Burst Core - when activated, the weapon will reload and automatically mag-dump every single round it can fire on full-automatic. When this occurs, an arc-like effect is seen on the weapon similar to the Amped XO-16, indicating the research that was conducted into electric rounds may have been incorporated into this new design. These Arc Rounds do not require the Burst Core to be active, however, and can be installed as a standard modification for the Monarch.
Other modifications for the XO16A2 include an Accelerator, allowing the Rate of Fire to ramp up over time, a Sniper Configuration that installs more advanced optics and tightens the weapon's spread and a Critical Hit modifier that increases damage dealt to enemy Titans.
The XO16A2 has the internal nickname "Shorty". This is due to the fact that the weapon has had its barrel shortened since the first game for CQC. It has also been re-coloured to match the paint scheme of BT-7274.
The A2's calibre is half that of the stated 1.6 inch calibre of the XOTBR-16 (approximately 40mm). However, given the inconsistency surrounding the portrayal of the ammunition used by the XO16 in the first game and the use of non-SI units (inches as opposed to mm), it is more likely that the A2 firing 20mm is a confirmation of the original weapon firing a 20mm cartridge.
For comparison, the projectile fired by the 40mm Cannon is much larger as seen in-game than that fired by either XO-16 model.
The reticle and crosshairs of the XO16A2 is much different from those of the XOTBR-16; the XO16A2's crosshairs feature 4 bars, 2 vertical and 2 horizontal, similar to the crosshairs of the R101C Carbine in Titanfall. It lacks a reticle entirely. The XOTBR-16's crosshairs feature the same design as the crosshairs of the XO16A2, but also have curved lines connecting each bar, which form a circular figure when aiming down sights. There is also a reticle.
At the launch of the Monarch's Reign DLC, the multiplayer version of the XO16A2 had only 35 without the Arc Rounds upgrade installed, similarly to the XO16A2 in the campaign's Expedition loadout for BT-7274. With the Arc Rounds upgrade installed, it had 45 ammo. However, in a later update, the XO16A2 was given 40 ammo without Arc Rounds, and 50 with Arc Rounds installed. The XO16A2 in the campaign has not received the ammunition buff that the multiplayer version did, however.
The XO16A2 has much less ammunition than the XOTBR-16; the XO16A2 has 40 ammo in multiplayer (50 with Arc Rounds installed), while the XOTBR-16 has 60 ammo, though it has 90 with Extended Magazine, and 150 with Accelerator.