I have recently had chronograph speeds on a 308 Win and a 17 Hornet that on the low end powder charges had speeds greater than the higher powder charges. Any ideas?

Since it happened to 2 different rifles I's say a Chronograph error. I had that once with a Chrony that I didn't have completely open.

Thanks. I will check that Chronograph along side another and see what happens.

Only time I had something like that happen is when I purposely worked up MAX loads. Once over a certain point (the MAX load), you'll often find additional powder to add no velocity or decrease velocity.