I peresonal have used a rock a stick a slinghsot, my then 300 Winmag (head shots) 870 WingMaster with 7-1/2 shot and of course now the Remington 1100 in 20 gauge with anything from 7-1/2 shot to number 4's .
The situation dictated the use of the weapon to take the grouse at the time.
I found that they where the hardest to hit was when they where on a kamikaze run from right to left at about 20 yrds and about 8 foot off the ground.
Buggah aced me on that one.
Rob