Muzzle Velocity & Barrel Length: Conversion Resources & Considerations

Question
Do you know of an online reference for converting muzzle velocity from one barrel length to another for a specified cartridge?  I believe I have seen such a page, but I am unable to concoct a search term that retrieves it.

Thank you for your service.

Answer
Here are some links I found, but not sure a calculator is out there since there are too many variables like bullet weight, twist, type of barrel, powder, round, weather, etc...


http://billstclair.com/energy.html

http://thefiringline.com/forums/showthread.php?t=212367

http://shooter.kndy.net/

http://www.gunandgame.com/forums/powder-keg/58175-barrel-length-muzzle-velocity.

http://www.riflebarrels.com/articles/50calibre/lengths_velocity_50_bmg.htm