Z-Jet baffles:
Suppressor cutaway pic - Page 2 - ArmsLocker Forums
Back when I worked for a gunsmith there were a lot of NFA owners who brought their toys over for show and tell. The quiet ones were always the larger cans, but modern advances seem to have let them shrink them down a bit and keep the same performance. About the tops for quiet was a co-axial design on a MAC11 subgun. About a foot long, 2" diameter outer over an 1 1/4" inner tube with standard M baffles stacked inside according to the owner. Sounded like a Singer Sewing Machine at max speed when fired, you heard the bolt clacking back and forth and that was about it.