A simple x-ray should confirm that.
If it reveals any voids or cavities in either projo {nota bene that older projectiles lke that sometimes utilized BASE fuzes, instead of nose fuzes}, or anything resembling a fuze inserted, your next call is probably the local police department's bomb squad.
Ideally, after you take the hit for carefully transporting them first to some suitably deserted spot like an old quarry or what-have-you (as opposed to having them come in and cordon off your house, the entire neighborhood, or the local dog & cat vet's office when you get the x-rays done. Someone who does you a solid by x-raying them will be remarkably less enthused when they find out the local cop shop will be descending upon their work premises like the Ride Of the Valkyries, and will probably tell you never to come back again. Your call there.)
Once their harmlessness is established, some careful caliper and scale measurements are in order, followed by making some polite contacts with online enthusiast forums, and/or places like the Artillery Museum at Ft. Sill OK, and/or the Ordnance Museum at Ft. Lee VA.
Back in the day at Swamp Lejeune, the base EOD techs kept up to date on everything going back to 1700s cannon balls, as locals were constantly unearthing everything deposited in the local landscape back to pre-Revolutionary times, and on more than one occasion, had discovered a still live Civil War or WWI-era explosive projectile dredged up by the blade of Farmer Brown's plow. It kept them on their toes in otherwise quiet times. A very polite query letter and suitable high-res photos (along with a SASE for a reply) may get you more information back than you know what to do with.
Once their provenance is established, marking the bases indelibly with that info, and noting that they're INERT in large block engraving, will save you and your heirs and assigns any number of headaches in decades to come, rather than going through this all over again someday.

At which point, I'd buff them out, and polish, paint, or plate them any way that suits you, including chroming, bronzing, or painting them up to resemble war shots (provided the base is discreetly but plainly marked otherwise).
And some example references:
http://thefiringline.com/forums/showthread.php?t=548825
http://cartridgecollectors.org/?page=in ... ll-casings