Emphatically no. 5.7 runs typically at 50,000, but the volumes involved are so small that even small setback, crimp, or charge deviations can send pressures to maximum or beyond (you'd better have a safety margin above 50k; Wiki says CIP requires it to be good to 125% of that, too)
The 5.7 has a very high impulse bolt thrust for its size due to this pressure, but it is very brief. This means the bolt weight:spring resistance ratio must be heavily tilted toward the bolt's weight, unless you are using a really long buffer tube.
If the spring is heavy enough to resist the bolt thrust itself, the bolt will be halted long before it can cycle fully since the chamber pressure is gone before it can build up enough momentum to overcome the spring. Cocking the action will also be hard to do manually, and the bolt will slam closed very violently. The spring also delivers the least force when you need it most; extended in battery. The bolt's contribution is always there, until the pressure drops and it is no longer needed to resist the thrust. If the bolt is heavy, it will be slow to get moving, like you want, and its great momentum will carry the bolt back to cycle the action, to smack your shoulder when it bottoms out in the tube. This is why simple blowbacks start to get really bad recoil mechanics in heavier calibers (people get cheek slap from 45ACP in CX4s). Since the 5.7x28 isn't a heavy caliber, the recoil would still be light, but you'd need a fairly heavy bolt. I've read that the PS90 has carbide weights in its bolt to get the mass it needs. People trying even slightly hotter hand-loads still need to add additional mass to get reliable function, though.
The Five-seven is indeed a delayed-blowback. The slide mass is not close to sufficient for simple blowback. It has several delays, in fact, which FNH had to use in conjunction with one another for the gun to operate--and it is a very narrow path the gun treads, albeit reliably. The cases are Teflon-coated to reduce friction and case stretch so head-separation isn't a constant threat. The barrel recoils with the bolt a short ways, the two locked together by the case-wall friction, and the neck blowing forward all the while.
It's hard enough to get even a 22WMR semi-auto to work safely and reliably. Ruger will no longer touch the subject. A 5.7x28 will have the same impediments, but more so. I'd want weights of the PS90 and Masterpiece Arms bolts/springs, as well as a summary of other delay-factors like friction or hammer-weight, before taking this idea much further. The little round is forced to operate on a knife edge between short cycling and rupture, and requires consistency in all things. If you must do it, start with the bolt as heavy as possible and shave it down from there until it works. Adding a heavier spring will do comparatively little to halt the instantaneous movement of the bolt under load, and will make the cycle much more violent.
TCB
