If you check Hodgdon Powder site you will find a few low pressure loads in the 7,500psi which is fairly low for a small bore. Just do a google search, enter site and go to 20 AA hulls.

Lead Shot 20 0.875 7/8 oz. 800-X Rem. 209P Rem. RXP 20 16.5 7,500 PSI 1200

Make sure that you check the site to find this load and make no substitutions. You want a bang not a boom.