Originally Posted by ar15barrels
It's the transistion that causes the problem.
If you get the bullet supersonic within the barrel, it's still going to travel where it's aimed.
When the bullet transistions back through is what causes the problem.
It the bullet never even goes supersonic, that's fine too.
You won't have to worry about it ever transitioning the sound barrier as the sound wave will always travel ahead of the bullet.
Thanks. Confirmed as I had time to look it up. Going transonic to supersonic or vice versa causes all kinds of instability problems.