Manufacturers almost always publish velocity and energyfigures with barrel lengths that maximize results. Most CF stats are with 26" test barrels that are longer than most sporting rifles. ML's are no different.
On the whole, you can expect your velocities to be lower per inch of barrel less than published. I won't guess at what it might be (OK - I'll take a guess - maybe 50-75 fps) - probaly someone with a chronograph will give you a more specific idea.