The guns are accurate enough for the magistrates, you can try re the calibration certificate, trained user etc but to be quite frank we are rather more switched on these days and have heard most loopholes.

Personally, if he was doing these speeds then he should just accept he was caught and take it like a man.

(mind you I have just had eight hours of people moaning when they are being caught speeding, jumping red lights and driving like fools so forgive me if I sound harsh)