Was I correct?
You're probably right. There are all manner of homemade silencers and/or methods, each of which is going to get the attention of ATF if you don't have the stamp (can you even get a stamp for a plastic soda bottle?) LOL
More likely, there's something more to the story of being able to convert by merely turning a screw. A shottie like that is probably going to get its own attention by the ATF since they frown on anything that would make a full auto conversion that easy (or even somewhat easy).
Considering the types of things they've cracked down on in the past...things you used to be able to buy but then they started going after the sellers (suppressor kits, ahem, I mean, solvent trap kits, or SBR/SBS that really aren't, but the ATF seemed to think so upon further reflection, even with ATF letters, etc).
Find out what shotgun that is and let us all know...we could either dispel the myth of an easy conversion, or see if it's the type of thing that's technically possible but is going to land you in a heap of trouble.
Thanks, at the time of the conversation, the teams had just been picked and I had to take the field.........I should see him Wednesday and I'll get more information about the shotgun.