I harvested an enormous amount of Autumn Beauty Sunflower Seeds in 2009. The weather was not ideal. There had been a lot of rain!  I had read that if you harvest them out of the seed head before they completely dry (and therefore develop) that the germination would be much poorer, but this had to be balanced against the fact that the birds then beat you to the harvest, in many instances... or even worse, that the mold would ruin them, so, I opted with getting the seed, in the first place. I carefully saved them, took the "extra" stuff out, and dried them down slowly. There was a half pound or so.   Later that winter, I ran my own little germination test on them.

The quick and dirty way to do that is:

• Take a given number of seeds, say 100, or whatever sample you feel will be indicative of a big enough sample to get a good reading, and lay them in a paper towel.
• Wet the paper towel, to mimic garden soil moisture, fold it around the seed, to cover them, and  put the whole thing into a ziploc bag on your kitchen counter or somewhere out of the way.....and check it beginning at three days until they sprout.
• After the "sprout period" for your type of seed has passed, count the number sprouted, take that as a percentage of the whole number you sampled, and voila! A percentage of viable seed is determined.

 My tests on my sunflower seed that I harvested was quite good for the species, I'm told, at around 75%,  sure enough, I had a plethora of sunflowers that year!  Price some of that seed....it's pretty expensive, making me all the more proud that I had some of my own.  Autumn Beauty Sunflowers, by the way, do breed true as they are not hybridized.  That makes it possible to save the seed with expectations that you will grow what you intended. :)