During the dry spell of small pistol primers, I bought small pistol "magnum" primers because I could not find the standard small pistol primers. Is it safe to use these in place of standard pistol primers by keeping the recommended powder charge at the low end? The intended use is in reloading 40 S&W for use in a XD 40 subcompact and 38 sp. to be used in a 357 Highway Patrolman.

Low end and work up a 1/10th of a grain. You should be fine.