Depends on the round used, the friction of the barrel, and the thermodynamic characteristics of that barrel. No one can given an answer. Just start writing down speeds over time. Ultimately, there should be a change as a new barrel "breaks in and settles down" no diferent than the horsepower of a car when first built versus the power of that car after the engine is broken in. Don't think anyone is really going to give you a better answer. Give it a couple hundred rounds and see what happens.So you don't know.
Got it.
Thank you.
-Stan