Yes, it can be legal to make a silencer. For everything Form-1, from silencer designs that are easily made, to filing forms with the BATF, to 3D modeling. Remember, you must have an approved BATF Form-1 to make a silencer. All NFA laws apply.
Long ago I ran across this most interesting YouTube that I have just reviewed for making
a long thin wall sleeve. The technique has many interesting applications for
projects such as protective sleeves, etc.