I would like to say firstly that I do not support the ill use of firearms upon innocent persons

The PAX 17: Mankind's first Multi barrelled monstrosity

Put Into service: 2172AD
Faction: Commonwealth
Type: Multi Barrelled Repeater

"The PAX, ahh yeah, this big guy is very useful! I remember once that we were ordered to raid a small asteroid base belonging to some pirates, when we dropped they started firing their weapons one way, just an endless barrage of Plasma fire, I managed to use my rcs to evade, when I started firing this thing, man, they scattered from their little nest, just shot after shot in a rather small area, pretty nice if I say so myself! We were then about to open their safe which was rather thick and nothing really worked, so one of our comrades used the upper kinetic barrel and...yeah, the hinges, were gone, I never thought kinetic rounds could be so devastating!"

-Daniel D. Russ, a Commonwealth trooper who participated in the raid of Derinar base of 2182, describing the effectiveness of the PAX 17

The PAX 17 MBR (Multi -Barrelled Repeater) is a reliable commonwealth gun design which was proposed on the 17th of October in 2171AD by PAX Arms manufacturers to replace the aging C-98 Handheld Plasma cannon (otherwise known as the Plasma slugger) by promising reliability, quick fire and innovative solutions which save time and increase longevity. During testing, the PAX-17 proved to be amongst the best and most reliable arms out of those tested hence earning it a place within the Commonwealths arsenal, thanks to its reliability, performance and it being a preference amongst soldiers, it has now become standard issued. This Plasma MBR fires both Kinetic high caliber (mostly used to penetrate through heavy armour and walls yet was made to ensure the gun was still usable after being hit with EMP the round is comparable to a 50 BMG) caseless ammo (to avoid a shell being thrown in your face or on your on the ground) via the upper barrel and Plasma via the bottom 2, hence making it a versatile weapons platform, as well, both Plasma barrels operate under chainfire principles to ensure that there is a constant barrage being fired at the target. Its braces by the barrels contain coolant to ensure that the barrels dont heat up quickly to ensure that the gun an still fire after a prolonged period of use, and it makes use of a plasma shot counter and an automatic hydrogen canister ejection system (contains 50 shots per canister) so that soldiers dont have to manually eject and reload to ensure time isnt wasted, yet there is a switch which de activates automatic reload should the system malfunction and eject canisters with shots remaining (hence the canisters having a larger back to make grip easier), as well as featuring an upper handle to handle recoil better and to ensure soldiers have a secure grip on the weapon itself to make reloading all mags easier without a heavy weight resting on top of your hand. The PAX-17 has many variants, The PAX-4, which fires a high energy plasma beam out of the top barrel, the PAX-15, which has all barrels fire plasma rounds and the PAX-Ares series, which is essentially all PAX Variants with attached knives and other improvements to make them worthy of fighting in wars against existential threats to Humanity.

Inspiration: Chiappa Triple threat Shotgun

Despite the PAX-17 Spawning in my head, my head likely based it off of the tri barrel design due to me seeing a .410 variant on an asmr channel. To put it briefly, the Chiappa triple threat is a break action (meaning one has to pull the barrels down in order to load the gun from the back) shotgun manufactured by Italian Arms manufacturers, Chiappa Firearms in 2013. It has 3 different variants which fire 3 different shotgun shell types, 12 gauge (tip with shotgun shells, the number represents the amount of lead balls in the shell if its buck, not too sure abt bird, if there is a smaller number shown, the lead balls compensate by being larger in size (with 10 gauge being the most dangerous (Idk if 4 gauge is in use nowadays)), in summary, smaller number=more dangerous), 20 gauge and .410 bore (the difference with 410 bore, is that it fires a slug (essentially a large projectile, not lead balls), hence its name is derived from its diameter, not lead ball count).

Credit: @TheVizzyLucky (saved me time and a headache, thanks brother!) and the creator of the "Umlimited aerogun" (no, I didnt spell wrong, that is the name)

I did use those XML'd engines since they imitated shots the best, so yeah.

As well id like to clarify, this isnt a gatling gun since it doesnt follow the rotary principle of a gatling gun (gatling guns rotate to alternate barrels to limit overheating allowing high rates of fire and direction removal, so im not just naming it something fancy lol...it doesnt work with real world logic unfortunately hence leading me to have to come up with a gun type for it)

AG's

Ag 1: switches off automatic ejection
Ag 4: Starts BRRT'ing

nonetheless,

Live Long and prosper and thank you!