Heavier bullets lose less velocity than lighter bullets in shorter barrels.
In my experience the opposite is true. But even then I'd not worry about it. I have 5 rifles in 308. One with an 18" barrel, one at 20" and the other 3 are 22".
Of the 3 the one with the 20" barrel on the Tikka CTR is the fastest. The 22" Bergara and Winchester are a little slower but all 3 are within 25-30 fps of each other. The Kimber is 25-30 fps slower than the other 3. The 18" Ruger Predator is about 75 fps slower than the Tikka, but less than 50 fps slower than the Kimber.
In other words don't let a 19" barrel decide which bullet you want to use.
