Too heavy for HARP. HARP was to put satellites into space orbit. The smaller 5 inch projo is a 5 inch 54 cal Hi-Frag that was designed to have a plastic obturator as a rotating band. It has a very aggressive knurl for that obturator to grip onto.
From all the features of the 8 inch projectiles, I would say they are experimental long range cargo projectiles after the design of the 155mm M864, and the EFRB base burner designs of Gerald Bull. They are missing the stabilizing pads around the body to keep their axes concentric as they travel down the bore, which is why they were never fired. Since the top of the boattail is knurled and they are missing a gilding metal rotating band, and they were found with the 5 inch 54 of that design, I would say they were intended to have a plastic obturator, except the knurling isn't aggressive enough. The gilding metal rotating band could have been on the rocket motor like the 8 inch M650, except the 650 had external threads on the body and internal threads on the rocket motor section and was full diameter.
Cargo could be HE fill, chemical, submunition, illum, nuke, etc. I say cargo because they have a screw in steel base plug, instead of a monoblock body of steel. The threads of the boattail base could be used to add a baseburner or rocket motor to increase range.
If you wash them off, and take a wire brush to the body, you should be able to find an XM or T number for experimental or Test respectively if they are Army or a Mk (Mark) and Mod number if they are Navy. The ID would be stamped into the bodies along with a manufacturer code and lot number that would include the manufacturing date.
Since they wouldn't be fired, they are most likely proof of concept projectiles, or very early incomplete design.
The U.S. phased out the 8 inch, most likely due to Russian pressure to eliminate the possibility of being able to slip a nuke inside.
Do they have a groove(s) machined down the inside wall? if so it they would be to keep the cargo from rotating inside.