My experience using 10's on woodcock--mentioned in John Alden Knight's book "Woodcock" (1944) as having been a pretty typical choice back then--was not a happy one. Also using 5/8 oz, but in a 28ga. Two birds dropped, got back up and flew again. One hit on a crossing shot looked like the breast had been liberally seasoned with pepper. I've killed a few early season grouse with 9's, and a few more with 8.5's. But I can't imagine using 10's on them.