Algodoo

Man, do you have densitophobia?!? (if that exists)
This gun can run perfectly at 100 Hz and with a real blowback if you decide to make everything heavier! My version of the short rifle test you did was heavier and worked better with less Hz than yours. things have to weight at least 11 or 2 kg for them to work well here!

Also recoil doesn't affect you at all unless you're doing this. So if you want to avoid scripts and make a realistic blowback you just have to make the bullets (projectiles) heavier, the bolt heavier too, and make the springs on the rounds stronger too. Then the bullet will go slower but you can compensate that with even more spring constant, or less weight on the bullet and more on the shell until it doesn't eject.

Also why don't you stack the rounds in the mag? you could get double the rounds there. my circular mag has 8 rounds more and is semicircular, actually

not worlking again