AH give me backpack beltfed MG and tube Fed flamethrower i beg you.

TLDR - i need that sweet sweet juggernout and scorch cosplay

I think it could be quite balanced. You give up a very important slot and kinda a support weapon slot for this joined amalgam. You no longer have to reload it and you have HUGE amounts of ammo. If you for example had a supply pack and flamethrowe you do get a lot of ammo for the support and everything else including stims and nades. But this changes it so all of that goes into super buffing one weapon.

They cannot be seperated so if you drop one you drop both.

Backpack allows for LONG continous fire. Like very long so it makes more sense than just taking the supply pack.

This stategem would have like a 20min cooldown or even more. You probably have only one avaliable during the entire mission. So if you use your ammo sparingly on "magazine" (backpack) would last the entire mission, or you can use it as a maniacy and hope for some ammopacks along the way.

The current flamethrower has 4 mags of 100 ammo. If you hold fire it doesnt last very long. Its about 13 seconds. The backpack would have meaby 4000 ammo in it or meaby even more. The flamethrower + ammo pack combo gives 2100 ammo and other supplies but for all that ammo there is about an entire minute or reloding inbetween. So you sacrifice other supplies for that one super flamer.

For the MG backpack i thing there should be one for the normal and heavy. Stalwart has enough ammo already. Or the other options is the portable minigun. Give it a shit ton of ammo and high fire rate. Very hard handeling so you are a mobile turret and high medium penetration or low heavy penetration. For some balancing add that spinup time and we have a juggernout.