I fired about 70 rounds of that Federal Powershok last Saturday. It consistently kept all 9 pellets inside the Q at 15 yards so that makes it a consistently 12 inch or smaller spread at 15 yards.
I ran a few rounds of RIO Royal 00 throughout the day and I was getting about 15 inches at 15 yards consistently, I wasn't getting any fliers though so that wasn't bad.
The Federal PowerShok seemed a bit more comfortable to shoot for some reason even though they are technically the same load I think, but I suppose thats the same as 2.75'' being 2.75" in a different brand.
I hereby recommend this as a good round at a good price:
http://www.ammunitiontogo.com/product_i ... 4-buckshot