I JUST got a Chronograph and I own the Nova Star .177 . I was using JSB Exact Beast Diabolo 16.20 grain pellets, or slugs. Not sure what they're technically called, but I have been getting 916 fps consistently on almost EVERY shot.
Like Steve said, this rifle thinks it's regulated.
It's more predictable than even my regulated air rifles !!
Just an AMAZING airgun. I love it, and was SO lucky to see it by accident on Amazon's one day sale. I got it new for half off. Amazing.
I highly recommend this air rifle to those that like a high shot count, good looks, and don't care about weight. It is heavy, but I only do bench shooting. Also, it's loud, so I have a Wolf Airguns silencer from Poland on it. I've ordered 3 from them. They have THE best selection and prices, just FYI on an unrelated side note.