Afternoon guys

This morning I chrono'd my HW97 for the first time this morning. I did it 10 times with JSB exact with a range of 724-735 fps. which by my maths takes it to 9.78-10.08 range. I checked my airwolf and HW77 which both gave 11.3 and 11.7 respectively, so I don't think it could be the chrono. The gun has had roughly 3000 pellets through so could it still be settling in or is it likely to be one of the rifles which has had the spring butchered?