Mark, my experience with SKB 500 20 ga is that the IC/M is plenty open for grouse and ducks. I brought down 11 blacks and mallards--bang, bang---as they rose from a pothole a couple years ago, estimated 30 yards. Retrieved crippled with my retriever. One over the limit but my buddy was with me so the law was only bruised. I use the 500 on everything from woodcock to geese.