Here is 12ga  prototype cushioned base sabot I put 
together to show how heavy of powder seal
and heavy cushion base that is needed. That
eliminates the blowouts and damage that was
happening to  sabots unless I put a  card 
under sabot. Just used a Brenekke seal/cushion
base, epoxied to bottom of sabot. Even fired one
and it got out the barrel and 437gr slug hit
 target straight. Ed