It is legal to make a gun without registration so long as it is just for your own use and does not fit in the “NFA” (machineguns etc) category.
thx for the clarification...
So, I can make a “zip gun” and the ATF has no problem?
Are you sure?
Because it seems to me the ATF was really interested in some folks’ “potato guns” a few years back:
“ATF has previously examined “potato guns” or “spud guns” as described above and has generally determined that such devices using potatoes as projectiles and used solely for recreational purposes are not weapons and do not meet the definition of “firearm” or “destructive device” in either the NFA or GCA. However, ATF has classified such devices as “firearms” and “destructive devices” if their design, construction, ammunition, actual use, or intended use indicate that they are weapons. For example, ATF has classified such devices as “firearms” and “destructive devices” if they are designed and used to expel flaming tennis balls.
Possession and use of “potato guns” or “spud guns” may be restricted under State laws and local ordinances. Further, any person intending to make, use, or transfer any such device must be aware that they have a potential for causing serious injury or damage.”