Jim,
This load is basically from "Reloading for Shotgunners" by Kurt Fackler/M.L. McPherson, 4th Edition, pg 161, but a little less charge.
Fed Gold Medal Paper hull
Fed 12S3 wad
17.5 gr Clays
Fed 209A
star crimp
In my singleshot Iver equipped with a Pressure Trace
http://www.shootingsoftware.com/pressure.htm straingage setup and chronograph, I measured about a 6500psi average and about 1150 fps average. You can try the 12S0 wad but I found it was a bit crowded and went with the 12S3. The book above lists a load of 18.0 gr Clays at 1180 fps, but doesn't list the pressure at this charge. They do list a 21 gr load a 1290 fps and 10,900.
I recommend you load 5 of these up and send them to the guy that Bell used in his tests, who's name now escapes me. But he tests for $5 a shot. I haven't done this, but have confidence in my test data. You'd be prudent to get a second source of pressure data.
