Please remember the pre sample MGs can only be kept if you are a sole proprietor. LLC, Corp, etc all have to dispose of the Pre Samples. A few years ago the pre samples were way cheaper than transferrables. After a rumor ATF was going to magically classify all pre samples as transferrables, the prices are now only slightly cheaper than transferrables in some cases.
07 with SOT does not have to file 5320.20 (interstate transport) Bring all your other paperwork. = NFA Handbook 13.8: ...." A person, other than an FFL/SOT, may not lawfully transport in interstate or foreign commerce any destructive device, machinegun, short-barreled shotgun, or short-barreled rifle, without prior written approval of ATF, specifically the NFA Branch."......
As mentioned, getting your 07 and paying SOT as a sole prop is a way of getting into post sample MGs but please realize unless you are a machinist and can weld, you will need either Law letters to buy post samples or will have to wait for an 07 to drop his SOT which allows him to sell them to other 07s with SOTs without a law enforcement "love letter". When this happens, the post samples sell for more than normal and they sell quickly. Expect first year setup costs of at least $5k: FFL, SOT reduced, ITAR, MA licenses, liability insurance. That is without rent, storage, cameras, alarm, data line required for MIRCS etc.
FYI: You have to do the manufacturing of the MG at your place of business, so going to a shop and having it done there (even while you wait) is illegal.
ITAR: Shops have been inspected and told to have ITAR paid by end of business day for that fiscal year and given X days to have ITAR paid for ALL years of operation or be prosecuted by the DOJ. I am not aware of an prosecutions immediately after the Fed finding out you have not paid it.