I loaded up some 100 gr horny psp's with 38 gr of H414 for my .243 and got a nice 1.5" group at 200 yds.A friend offer his chronograph and I got an average of 2600 fps for three rounds.My book shows 2960 fps with their 24" test bbl.I know that my round would be slower but by this much?Max load for H414/100gr bullet in .243 is 40 grns.My bbl legnth is 22".Any one have some answers as to what the velocity shed rate is per bbl legnth.  

I don't have one available right now, but the commercial ammo printouts from Winchester and Remington usually have an adjustment factor of something like 30-50 fps per inch of barrel.  Two inches of barrel certainly should not be dropping your velocity 360fps at the 22 inch length.  Is the 2960 fps velocity given for your 38 gr powder load or for the heavier 40 gr load? That could make quite a bit of difference in the load's velocity.  The barrel length alone should not make that large of a difference.   Watch-Six

Some things to consider:
- How far away from the muzzle are you measuring from (and at what distance are the values in the book measured from) and under what atmospheric conditions?  That would count for some of it (though certaintly not 300fps worth)

- Could the book have a typo?  (check another manufacuters reloading manual)

- Could the Chrono have a problem?  Try it with another load where you have the manufacturers velocity listed (to verify calibration).

- Are you sure you loaded with the proper powder?  Were you doing any other loading at that time?

Thanks Watch Six and Forest,guess I've got to do some home work.Yes,the listed velocity is at 40 grns of H414.The chrono wasn't mine, but was placed about 5 feet from the muzzle.Weather wasn't a factor: low humidity,no wind, mild temps.My brass shows or primers show no pressure signs, guess I'll go to 40 grns and magnum primers and see if I don't get some more zip out of it.Load data comes out of Hodgdon manual.Thanks for your input.