I would suggest looking up a topic called "moment of inertia." Fact is, a rod spun about its axis doesn't absorb a whole lot of energy/momentum/etc in so doing. Not compared to spinning it perpendicular (like a baton) or even reciprocating it back & forth like a piston. The reason is because the metal at/near the center of the rotation doesn't actually rotate much, so the effect is nearly identical to spinning a hollow tube of lighter mass.
So if you're going to accelerate a bolt mass to make it absorb more energy over a given distance so the bolt can be lighter for a given cartridge, it makes the most sense to spin it orthogonal to its length, and reciprocate it, in that order (there's a weird little piston/crank Mauser SMG that sort of works like this).
The layout of your concept gun looks cool, but the mag appears to be 223 or even 308 type rifle cartridge length; I'd cool my aspirations to pistol cartridges first to feel out the effectiveness of these ideas before pursuing them in such high powered options --you can't afford to be "close" with that kind of juice, and delayed blowback is always a dance with the devil, no matter how you go about it.
Another route might be to make the action recoil operated; most delayed blowback systems like the FAMAS or CETME actually started out as recoil-operated formats (Federov and MG42 if memory serves), and a screw-delay turned into a recoil-op locked breech is what we call "rotating bolt" lockup and highly reliable, so it may be possible to work it into a blowback with careful design & development.
TCB