Col. Stoll was very interested in the new 5,56 NATO round and wanted to conduct further experiments but during the early 1960’s, no 5.56 barrels were available at the Felixdorf Proving Grounds, so he used regular .30 M1 cases with a white plastic sabot loaded with standard 5.56 bullets. This was a short lived project because 5.56 barrels became available and there were problems with the loadings because they could not get reliable bullet/sabot separation.