While the 20mm and 37mm cases have been shown on a recent thread, I thought it might be interesting to see them side by side to show the difference in size. (And I’m happy to have the 20mm as a new addition…)
Note the 37mm XM446E2 here has no “Zone” indication.
The 20mm XM101 was fired from the spotting rifle (XM-69?) mounted to the 120mm XM28 recoilless gun. The 37mm was used in the XM77 spotting gun (which I believe was smooth bored) mounted to the 155mm XM29 recoilless gun. Both recoilless guns were designed to launch the same nuclear projectile to a range of about 1.5 and 2.5 miles respectively.
Pete deCoux was kind enough to show some interesting 20mm variations in the above mentioned thread viewtopic.php?f=8&t=16897 and Zac (cartguy) showed an XM446E2 37mm Zone II. Any other variations out there?