The firearms examiner that looks it over before trial will certainly know what it is (he will also check to see if it was ever stolen, etc). There are a couple of points worth mentioning: first is that what you want to build violates federal laws, the first being manufacture of an illegal weapon, the second that it would be classified as "Any Other Weapon" under ATF rules and require a tax stamp with the requisite background check and signature from the chief LEO in your area to possess it. Figure ten years each in federal prison as a good guideline, plus the potential for state charges. I would also add that one should stick to weapons that won't make a jury think that you are an evil person. You want to look like, and indeed be, a law abiding person should your peers ever have to decide your guilt or innocence. Whatever you use/carry should be legal in your jurisdiction, and you should follow the rules for carry and/or use.

Finally, you needn't be paranoid in life, but you should be aware of what is going on around you all the time, and even more so if you carry a weapon. I have no problem with people choosing to carry legal means of defense, but remember that if you do, there will be a weapon at every potential conflict. In addition to knowing how to use it, you had better know how to retain it. I personally think that most state CCW courses are a joke. If you want to carry, plan to attend a quality firearms school (LFI, Gunsite, TDI, etc) where they will address more than state firearms law and firing a few rounds on a square range.