I'm under the impression that most 9mm uppers run as blowback operation as opposed to DI.  Is anyone running a blowback system without a buffer?

It sure would be neat for my next build to be a 9mm SBR with a folding stock.

Anybody else have this idea before?

They're blowback, but they still need a spring and buffer.
Unless the spring is integral to the upper, a sidefolder is a non-starter.
Blowback .22s work because of the short stroke and self contained nature of the bolt assembly, none of which ever moves past the rear of the upper.
Pistol caliber setups typically have a bolt carrier just like DI .223 setups, whether blowback of DI. this recoils into the buffer tube the same as normal DI .223 setups.

Have another beer and come up with another idea.

working on the beer part now.

thanks for the replies.  it was just something i had stuck in the back of my mind.  i guess i'll have to shift my side folder ideas back down to 22lr.