I just submitted a form 1 for a .22 can yesterday.
I added in the description that I was going to CNC it out of bar stock aluminum, and that I have no parts or tools on hand. I also specified that I was not building one out of a kit or 80%. For the picture, I literally just put a picture of barstock on there.
I didn't attach a picture of the drawing, design, or anything like that. So we'll see what they end up saying.
Efile form 1, with a .eft fingerprint card. Should only take 35 or so days to hear an answer, so we'll see.
I don't think you attaching a drawing will hurt anything, OP.
ETA I went back and pulled my description and Why Make:
TO BE CNC MILLED COMPLETELY FROM BAR STOCK ALUMINUM, NO KIT. THREADED CAP, BAFFLES, ENDCAP, AND TUBE.
FOR ALL LEGAL PURPOSES, INCLUDING TESTING OF A BAFFLE DESIGN FOR PERSONAL USE ONLY. NO MATERIALS ON HAND AS OF FILING, NO TOOLS ON HAND AS OF FILING.