Originally Posted by Jim K
There is no FEDERAL requirement that you carry the registration document (Form 4 or equivalent) with you when you take the gun off your property, only that it be made available to an ATF agent on request. BUT, having that paper might protect you from hassle by local police. I say "might" because some police are totally ignorant of firearms law and believe that all machineguns are illegal, or should be, and will arrest anyone with such a weapon.
Jim K is correct, there is no federal requirement that you carry the paperwork with you. You do not have to show the Form 4 to LE/range master/local "know it all" as it is actually considered a private tax document. Tho showing it usually gets you out of alot of hassle.
I routinely attend MG shoots here in NV with 20+ MGs/suppressors/SBR/SBS/etc and don't bother carrying any of my paperwork.
Example: I was the first to shoot MGs at a private range back east and sure enough shortly after i let loose the first time I had officers from two towns (the town line ran through the club) show up. They knew nothing about MGs or the Federal/State law. As soon as i showed them the paperwork with the ATF letterhead and signature they could have cared less.