Plastic / nylon sabots are still around. Google sabot accellerator and you should find some hits.
A few points you may want to consider:
1: not for short range
Sabots take between 25 to 50 yards to reliably separate from their payload.
2: crown critical
These things begin to open up upon leaving the muzzle. The crown of your rifle is critical to accuracy.
3: squeaky clean!
Sabots LOVE squaky clean, no fouling, fresh bare steel barrels. The plastic they are made of is softer than the copper that could be fouling the rifling of a barrel, and that fouling can and will scrape and cause irregularities in the sabot that can impact accuracy.
Be sure that you are stabelizing the sub caliber payload properly, or accuracy may suffer!
5: Muzzle break
I have heard no definite reports, but it seems a bad idea to fire this flowering, expanding bit of nylon through a baffled muzzle break. This, by the way, is the reason I still havn't tried a .50 sabot down to .30. Imagine, 4900 FPS with a 250 Gr .308 bullet! But without a really good break, kiss your shoulder goodbye! Maybe in a really big railgun type setup, but not shoulder fired!