Nitro, these were some of the better fun rounds produced,they all so came in 30-30, and I shot a box car full of them at ground hogs off the back of a buddy'e tractor.
Haveing talked with some of the older Remington upper echlon
and the main reason at the time they dropped them was due to the heavy pressure from the ATF, there had been a very few shootings with these and they were trying to shut down the so called perfect non traceable bullet.
EABrown here in the States sells a kit to use the Sabot and the flat base 224 bullet, and I have tried loads in just about any thing 30 cal wise that they will fit in, they can be a lot of fun. I like your idea of useing either 6mm or 7mm bullets to