Been off-forum for a while during Covid etc. and trying to catch up.
While these items are not marked correctly, they appear to be SETH warheads (Simulation Equipment Test Hardware). The UN chemical weapons treaty was quite strict on empty chemical weapons being among the first items destroyed, and as the US lagged behind (domestic lawsuits) on their destruction efforts, they needed inert munitions during destruction facility trials, to simulate weapons passing through the process and work out any problems. Agreements were struck, and the US manufactured (copy) munitions for this purpose, normally made from converted HE rounds, bronze in color and marked as SETH and with the designation of the item it was simulating. Many junior collectors obtain these items and mistakenly believe that they have original chemical weapons. Among the most common are the 105mm M360 or M60, the 155mm M121 and the 4.2-inch M2 mortar.