Wow! My neighbors better be on their toes! If any zombies attack my house I might just be launching slugs that take a 90 degree turn when they exit my barrel!
Come on now, let's be realistic. I've never fired anything out of my shotgun (in 20 years of heavy use) that performed so insanely opposite of what I expected that I would deem it unsafe.
Fact is, you've installed a new bbl. you've admittedly never fired so you have no idea where your projectile(whatever they are) are going to hit. Missing a paper plate by a couple inch's with a slug at 20yds. will be several feet off at 100-150yds.
Far as safety goes, this is really a moot discussion at this point.
Good luck and have fun getting acquainted with your new setup.