Because it is more challenging to make a long kill.
And if you go to a gun choked tight emough so you can go to larger shot so you have penetration and a gun heavy enough so you can go to more ounces of shot you can have the same kill circle at sixty yards that you do shooting a lighter load through an open choked gun at 30 yards.
Although shooting a pheasant at 60 yards with an 1-1/8 oz of 7-1/2s through a cylinder choke seems likely to wound shooting a goose at 70 yards with 2oz of #2s at 70 yards through a 40/1000th choke might be a fatal long range combination.
Best,
Mike
Last edited by AmarilloMike; 03/03/10 08:21 PM.