And here is my 835 at the same distance with what amounts to a similar shell.

Mossberg 835 Grand Slam
Pure Gold .670
Hevi-13 1 3/4oz #6
40 yards
207 hits in 10" with 391 hits total = 52.9%




Looking at the %... you can draw a loose conclusion that my 12 is shooting about 10% tighter at 40 yards than my 20 gauge.... but what you really have to take into consideration is the sheer volume of pellets.... it has twice the number of 10" hits as well as twice the number of total pellets anyway.

That same gun and load with a different choke tube gave me 86 in a 10" with 263 total at 70 yards. I weighed the average (because I shot left a bit and I know several pellets missed the square yard sheet of paper) and came out with 32.6%. At about $4 a shell... I wasn't about to redo the test in the name of science. That will still kill a bird very much dead.... but the center of my pattern was about 15" left of where it should have been. It comes down to the you factor a lot more at range... and I just won't do it. No different than with a bow.... so many little things get magnified past 50 yards.