I.B.O. speeds are measured using a bow set at 70lbs with a 30" drawlength, using a 350gr arrow, with no kisser or loop (also using a "mechanical archer" for consistency). 264fps doesn't sound out of the question with your set-up. Is the chronograph just a few inches in front of the bow? You should be shooting thru it at point-blank range. Myset-up shoots 271fps.