I hope Remington STS Target Hulls are brass. The new WIN AA's suck monkey balls for reloading.
Most of the game loads are brass plated steel, they don't seal the chamber as well as brass and therefore are dirtier to shoot.
I've ran across lots ( 100+) of once fired WIN steel base target shells with the primer already out. A friend picked them up at Algonac State Park.
Keep an eye out for primer pressure, just as one would do working up a target load.
In this time of low supply, buy and shoot what you can find.