For the initial test I used 25.5 grs. of Reloader#7 which is about 1.0 grs. under the Max load listed for 123 gr. J bullets in the Lyman manual. No pressure issues since the sabot/bullet are just under one half the weight of the standard factory bullet and the sabot itself is slightly undersized and tends to mimic the characteristics of a cast bullet rather than a jacketed bullet.
I've only done the one test so your results may vary,I do plan to work on some other loads using different powder/bullet combination and do some accuracy testing along with chrono data. The initial load I had worked up pushed the little 52 gr. bullet at around 2800 fps. average on my friends chrono. On a side note make sure that you don't shoot sabots in any firearm that has a muzzle attachment such as a brake or suppressor.