Awww, the moment I read ww1/2 I was out of ideas cx

Otherwise you could go with a banana-based minigun and call it "the monkey business"

Would there have been much use for an SMG-sized weapon which used 30-round magazines which used heavy machine gun ammo with a 600 rpm firing speed? I'm guessing the recoil and lack of barrel length would make it inaccurate but I was thinking it could be useful for suppression fire and clearing relatively soft cover.

Do you define HMG as high calibre or heavy weight MG?

I'm not fully sure. Probably high calibre considering what the weapon would be used for.

wouldnt an LSW do the same with more managable ammo?

That would be slightly less original. :P And my idea is for this to be a bit more portable than an LSW (if those are smaller machine guns).

Real weapons or fictional?

Fictional ideas derived from real

V3 England Gun THe largest proposed gun ever. Capable of launching a 50 kilo payload to near orbital speeds

How do you solve the obturation issue with accelerator cannon design?

I Assume the shell,(which is a multitonshell) is longer than the holes so it slides past them

Actually the thing was a huge flechette with fins, ergo the obturation issue