The circle comes after the shot. Here's the method.
Take a 4'X4' piece of blank paper, affix a small dot in the middle for an aiming point(Which you will NOT aim at) and MEASURE or pace off the distance you want.
40 yards is traditional, but I suggest patterning where you take your birds at. For upland stuff, 25 or 30 yards is more common.
Anyway, look at the aiming point, mount your shotgun and fire as if it was flying. Do not aim.
Repeat a few times on fresh papaer, marking the old ones as to choke, load, bbl or other cogent info.
Now take them all home and spread out the first one on a flat surface.
Look for the densest part, the core. Note it's relation to the POA. This tells whether your shotgun and you shoot high, low, etc.
Now, knot two pencils in a piece of string 10" apart.Stick one in that densest area and scribe a circle around it with the other. Next, reknot the pencils 15" apart and scribe a second circle. Now, grab a felt marker and start counting. When you have all the pellets in the smaller circle counted, count the ones in the larger. Mark down the totals, divide by the total number of pellets in the load to get the percentage. More cogent, note any holes in the pattern big enough to let a bird through. Call that 4 inches. If there's 2 holes that size or less, your patterns will work at that range with that load. Also note the holes in the outer ring, lots of pellets here means more inches of working pattern.
Hope this helps, tho I think Geoff did a better job not too long ago...
