i have always used #4 shot with my turkey tubes.fed prem,win supreme and hevishot with great success.as already pointed out,different tubes and loads perform differently.i just sent a barrel to carlsons chokes and had it cut down to 22" and a tube installed for #4 shot which was .670.i have not patterned it yet,but they recommended the .670 for #4 shot. from what i understand, if you want to shoot #6 start with a .660 tube,#5 would be .665 and #4 would be .670.this does not mean that a particular brand or load will perform well in your gun.that's why you have to find out what tube and load works best in your gun.if all three major brands of #4s do not suit me with this .670 tube,i will try all three in #5s until i find the one that gives the best pattern.