I have shot many flats of 7/8 oz loads in a 16 ga. I use 17.5 grains of Green Dot. So pressure with 7/8 is certainly under 9,000 psi. Check out the Reliant Reloaders Guide

Remington case
209 Winchester primer or Cheddite
Gualandi Wad from Grafs

Perfect fit for the Remington case a very good load for target and small birds. If ordering wads from Graf, order the one that holds 1 oz of shot, not the one for 1-1 1/8.