This is a pretty rare item you will likely never see in the wild. These were made and issued out for US Army Snipers for use in Vietnam. You stick the sharp end into the ground and rest the XM21 rifle in the top green more rounded “U.” It must not have been very popular. Unlike bipods attached to a rifle you cant just pick up the rifle and set it down or move it as needed and I can’t imagine pushing that down in the ground while trying to be quiet was very appealing, Also likely hard to remember to grab it if you had to move fast.

You can see it in a US Army manual for Sniper equipment. This was republished in one of Senich’s books but I have no idea what training guide he got it from.