Don't believe the PB could be considered a sabot any more then any other 'full caliber' bullet with a gas check/seal. Course with some of the different screwy state laws, it wouldn't surprise me any.
Far as shooting the PB's, they shoot very well in some rifles, others not so much.
My Optima shoots them very well as did the Wolf I had. I know of two other Optima's that sling PB's very well.
NOTE: All these rifle's tend to start loosing accuracy shooting PB's with charges higher than 120grns.
The Omega I had did just ok with them but shot sabots way better. The Encore I currently have will not shoot them at all but will drive tacks with sabots.
I have not tried other 'full caliber' bullets I.E. maxi ball/maxi hunter out of the Encore.