I shot shot my first 20 shots from a detuned Ruger AirHawk right off the shelf from Bass Pro. Walked to the shelf. Picked it up and paid for it at the desk no questions asked. Let it sit for months and today I decided to chrony it. (And the breech seal looks dead flush with the breech.) The barrel is 6 feet from the chrony. I'm getting a consistent 540+. Consistent for twenty shots! Why? What's going on here? Any words from the wise on this one?

Thanks

PS - Sounds "hollow" when it fires. Is this the sound of a bleed hole?