you might not have too much joy with the chrono,they were apparently designed to use the dieselling effect,and tend to be smokey,(mine is),and thereby fool the chrono,I'd be interested to hear what anyone else has to say on that.I've read dozens of articles over the years,and power is quoted anywhere between 8 and 28ft/lbs,all I can say is my father shot one regularly on a farm in the 30's,and said it was a hell of a lot more powerful than the airsporter he bought me as a teenager.