A few years ago my son stopped by a pawn shop in another state and picked up a ProChrono jr chronograph for me. I have not used it a great deal, but have timed some rimfires.
  Yesterday, my grandson and I were doing some zeroing in a nearby gravel pit. We used some .44 mag handloads we had completed. 
     Used Hornady 240 gr XTP hollowpoints, pushed by 24 gr IMR4227..Nice accuracy...1706 fps...pleased.
   Then I tried my .223 Rem..65 gr Sierra Gamekings, 26 gr Varget, should be between 2900-3100 fps...but I couldn't get a reading..no reaction from the chrony.
   Conditions.. temperature above freezing, overcast, virtually no wind, shooting from prone...ground still frozen with rough tracks from Cat hi-lift so chrony did not sit really level
   
       Are these not good for .223 speed ?