The same is true of the combination of the AR pistol upper with the AR rifle lower. If you have both of them apart, you are in constructive possession of a short barreled rifle, even though you had no intention to illegally assemble one. So clean them at different times, or leave the forward pin in place so the receivers stay together.
Far fetched? I was the E.M.T. at a fire standby years ago. The fire was quickly extinguished, but the firefighters sent in a team to break down the area and make sure the fire was out. They found a quarter pound of pot. The homeowners were arrested and charged with intent to distribute.
Stranger things have happened. A friend was on a fire standby when they found a very active World War II trophy in the homeowner’s attic. It was either an MP-40 or the aforementioned StG-44. I never found out which one. Fortunately, the guy was old enough, and tired enough, that the cops just took it and declined to prosecute. Unfortunately, the cops just took it and since it was in New Jersey, I'm sure the thing was destroyed.
Thanks. I appreciate the confirmation of what I was told.