Poking around on the Web a little, I'd say it should have been made in the late 1930s to mid 1950s. (
http://www.thehighroad.org/showthread.php?t=98768 ) Not really all that old as guns go. If it's made for modern smokeless powder ammo, and is tight mechanically, it should be fine. The payload in the buckshot shell shouldn't actually weigh more than birdshot after all. And the powder charge should be approximately the same also, or should be indicated 'maximum load' or such on the box.
000 buck is .350" in diameter, even with full chokes (and I think your double is likely full and full, if it's original) the diameter of the buckshot shouldn't be a problem in a .410" bore. Full choke is mostly listed as .030" constriction, so .410"- .030" = .380". Getting a string of .35" projectiles out of a .38" muzzle should not present a problem your gun can't handle, assuming it's in good shape otherwise.
You can use the 'fencepost test' if you're really worried about it- tie the gun securely to a post in such a way that it won't get scratched/damaged when fired, muzzles securely upright, and pull the trigger from a safe distance/from behind cover with a string(s). Or have a local 'smith check it out for you- more scientific, but costs more too... .
As to the safety thing, my mom kept a little 20 ga. Stevens 311 that I cut down to fit her handy for a long time with chambers loaded and safety on for years. Restricting access to the gun is the safety issue when it is primed and ready to fire just by taking the safety off. She kept her shotgun well hidden in case anyone got in the house so it wouldn't get stolen, I suggest you find a good place for yours that is out of sight yet easily accessible. I don't want to disclose her hiding place here but go over your bedroom thinking like a smash-and-grab thief, and see what hiding places you can find or relatively easily make.
hth,
lpl/nc