22LR maximum chamber pressure is 170 MPa. 7.62x39 is over 310 MPa. Doing some napkin math with pressure and case size can give an upper limit for force on the bolt. For 22LR that's about 450 kgf. For 7.62 it's about 3200 kgf. Actual is less, but the relationship holds, so you'd need a bolt locking mechanism over 7 times stronger than the SR722. Generally speaking that's going to mean machining something out of relatively high grade (and probably heat treated) steel.

Right now 9mm is about as powerful as you can get in a DIY firearm with no commercial gun parts and no machined metal parts. There's also the problem of forming the barrel/chamber since there isn't currently a good way to ECM a chamber for a bottleneck cartridge. That's not to say it can't be done, but it hasn't been done yet and I don't think you'll see rapid progress due to cost and safety considerations.