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.
I am going to build suppressor for my Tikka and would to ask which design is the most efficient? Has anyone drawing / design guide which dimensions are important?