Ok, your RED sabot looks orange on my screen. It is not the same sabot as the White TAN sabot. Look closer.
It may have been made from a modified White sabot mold that removed the rings from the outside of the base, and I suspect that the bottom of the bullet cup was probably modified for a flat based bullet as well.
Either I'm having a serious case of deja vu, or weave hashed this out once before?
You cannot shoot a flat based brass bullet in a White Sabot and expect it to survive. Just loading it into the barrel will severely compromise the walls below the petals, making them thin from the force it would take to push the bullet into the bottom of the bullet cup and system your bore. If you didn't get the bullet to push through the chamfered portion in the bottom of the bullet cup, when you shoot it, it certainly isn't going to make it better.
Those .45 cal White TAN sabots were made for the 350 grain swaged lead .40 cal boatailed bullets, and they shoot just fine with any BP or BP Substitute. Except if you are shooting a .45 caliber Knight Elite 1:30 twist with a piss poor factory crown.