to work out what your fps should be if you switch from JSB Exacts to JSB Heavies, to JSB Exact Expresses or Webly Mosquitos as they are known in the UK Chris Cundey's Pellet fps to ftlb conversion table
Just found this and it looks pretty damned useful when fine tuning velocities in none AT rifles! Andy
Here's a version of Chris' spreadsheet with an extra pellet type, fewer unnecessary columns and a calculator for determining the threshold velocities for 12 and 20 ft-lb limits. You can download it here.
I've edited mine and saved it as a share. Mine only has the 4 JSB variants ( RS, express, exact, heavy) listed. All formulas are still there but now hidden so you only see FPS and Ft/lbs: LINKAGE If anyone would like a copy as an ms excel file pm me your email and i will send it. I will even add pellet of your choice