I usually just cut open a shell and count pellets. There's enough difference in pellet count between an ounce (or whatever) of 7 1/2's and 8's that you should be able to tell the difference without much problem. Even without a mike, if you have American shot size whatever, you can always do an eyeball comparison to foreign loads that contain the same shot size you're comparing to--at least according to what it says on the box.