When dabbling in shot sizes in order to compare apples to apples it is best to use SI units or say mm. If I recall correctly, Gamebore Diamond shot sizes are as follows:

#4s - 3.25mm
#5s - 3.0mm
#6s - 2.8mm

I know I have some #7s(2.4mm) and may have some #6s that I'd cut open & measure if need be.

Cheers,

Raimey
rse