I'd be interested in knowing the history, where did you get it, what were you told about it, etc etc.
If I didn't know anything about it I'd do just as you done and take it to a gun shop / smith and ask them about it. If they said it's unsafe I certainly wouldn't shoot it, but I'd be even more interested in knowing more about it.
As stated, hand loading something for it could well be what it was intended for. I have thought about doing such things but often thought how dangerous my kitchen gun-smithing would be to someone else not knowing what I had done it for.
Same could be said for many black powder collections around, guys have conversion cylinders laying around, 45 acp, 44 magnums, hand loads, etc etc. Brass frame revolvers, steel frame revolvers, old shotguns that could never withstand what that new Browning sitting right beside it does, or the shells on the shelf above it. Even though they chamber in it just fine.
What I'm saying is, someone could have, and likely did, do this for a reason, and it was likely safe for what he intended. You just need to find out what that was and stick to it
Be safe!