Carved into the side of the rifle are the words "Armor Nulifying Tungsten Infused Munition Accelerating Toward Every Retrobate In Affected Line." 

You have a +2 bonus to attack and damage rolls made with this magic weapon. This weapon is made of a solid, dark grey material with a scope mounted on top of the chassis, and a stabilizing device is attached to the front of the under barrel. This weapon has two configuration modes: Rifle and Sniper. While in the Rifle mode, it can be fired while standing, using its normal ranges as listed. While in rifle mode, you can only use the mode: Overcharge. Its second configuration is Sniper. While in this mode, you must be prone on the ground and have the bipod extended. While in Sniper mode, you can treat this as a +4 weapon; its effective and max ranges have also increased to 200/600, and you gain access to the mode: Ubercharge and Ultracharge. Mode: overcharge, ubercharge, and ultracharge can only be used with the special tungsten rounds made for the weapon. Normal ammunition can be used with the weapon. However, the weapon's damage goes down to 2d8 + Dexterity modifier. This weapon also over-penetrates targets. Up to two additional targets behind the first in a 15 ft line starting from the target can be affected by the bullet. The targets hit by the round are only able to take up to half the damage dealt, regardless of the mode used, except for ultracharge. If additional targets are hit by an ultracharge shot, they are also subject to the correlating damage of the primary target. For the round to hit the other targets, the attack roll must have also hit their AC or higher. That target may also use the shield spell or other AC-raising reactions to raise their AC against the attack unless they are surprised. 

Mode: Overcharge. When you overcharge a piece of ammunition, the weapon gains an increased critical range and an increased misfire range. The weapon's increased critical range is 18-20. Its misfire range is 1-5. 

Mode: Ubercharge. When you ubercharge a piece of ammunition, the weapon's critical and misfire ranges increase even further. The weapon's critical range is increased to 16-20, and its misfire range is increased from 2-7. If you roll a natural 1, regardless of the rules used, the ammunition explodes in the rifle and backfires on the user, dealing normal weapon damage to the user. As well as that, the gun cannot be used again for 1 minute, allowing the gun to cool down. 

Mode: Ultracharge. When you ultracharge a piece of ammunition, the weapon is pushed to its absolute limit. The weapon's critical range is increased to 14-20 and deals triple weapon damage. Its misfire range is increased to 6-8. the weapons backfire failure is increased to a 1-5 and deals critical damage to the user. 

It’s up to you to decide whether a character has proficiency with a firearm. Characters in most D&D worlds wouldn’t have such proficiency. During their downtime, characters can use the training rules in the Player’s Handbook to acquire proficiency, assuming that they have enough ammunition to keep the weapons working while mastering their use.

Notes: Bonus: Magic, Damage, Combat, Range, Two-Handed, Ammunition (Firearms), Reload, Sap