Mabeknot wrote:
> My only real concern is, is it safe? If there's any chance there might be powder in it.
Going by your description and measurements, it is not a cannonball, and it's way too big to be handgrenade, and too small to be a landmine ...so the odds are just about as conclusive as can be that it is not an Explosive Device.
Furthermore, its Diameter-To-Weight Ratio (which I used in order to calculate its shellwall-thickness) very strongly indicates that there's nothing but empty space inside it.
A brief explanation of Diameter-To-Weight Ratio:
It is possible to calculate the wall-thickness of a hollow "perfect sphere" when you know
(1) its diameter,
(2) its weight, and
(3) the Specific Gravity of the material it is made of.
You said its diameter is 4-&-7/8 inches, it weighs 5 pounds, and I used the Specific Gravity of iron to do the calculation.
The extra-precise sizes and weights of all American civil war (and Revolutionary War) solid-shot Iron cannonballs (and SOME of the hollow ones) can be viewed online, for free, at
Descriptions of shot for smoothbore guns
As to what the item is... since its precise size, weight, and characteristics (it has TWO 1-&-1/2-inch plugs) don't match up with any artillery projectile, grenade, landmine, or Sports Shot Put, I am left with guessing it is some kind of Industrial object, perhaps a machinery counterweight. You haven't mentioned any markings on it, so I assume it has none.
At this point, all I can suggest is that you take some good (well-focused) CLOSE-UP digital-camera photos of it (and the two plugs in it), and post the photos. Perhaps somebody here will recognize it.
Regards,
Pete [P.C. George]