As the owner of H&K USPc in .40 and .45, they are nice guns (and your price is good) but not something that I'd run out and buy for carrying purposes (the few that are available in MA by private sale typically go for $800-900 used with low-cap mags). After running ~600 rds in 3 days during a defensive handgun tactics course last Summer (and another 1K rds after the course) I learned a lot about that gun (I shot the .40) . . . that the trigger does NOT contribute well to accuracy or effective trigger reset. I've discussed the issue with H&K in VA and some gunsmiths subsequently and there aren't a lot of good options. Therefore, I've retired those guns to my safe and am carrying the Walther P99 .40 and S&W 1911 .45 these days and will use the 1911 for two upcoming courses over the next 5 weeks (3-day est ~600 rds in June and 4-day est 1K rds in July) and bringing the P99 as a backup (in case of any failure of the 1911).
I'd guess that the OP is a non-MA FFL since MGLs in 1998 did NOT include a LE exemption on the sale of handguns that aren't on the EOPS "List" {ref C 140 S 123 eighteenth and following paragraphs). On letterhead, the agency can purchase guns from any FFL in the US (except MA FFLs), but MA FFLs can't legally sell them any guns that aren't on the List. I doubt that the AG would prosecute on a LE sale since that would be "career limiting" to his ambitions to become total czar of MA, however reading Ch. 180 of the Acts of 1998 (now incorporated into Ch. 140 MGLs) you can see that there is no LE exemption. The AG's regs do exempt LE agency or LEO handguns from his "product safety" regs, but the law doesn't track the same.
Full-Auto:
- MGLs allow a MG Permit to be issued to ONLY two classes of people (again changed in 1998): certified LE firearms instructors and/or "bona-fide collectors" (a C&R FFL qualifies you). That is the MA permit you need to possess one. Since it is a discretionary permit, there are some chiefs who will absolutely refuse to issue them, so you need to do some checking first.
- Fed paperwork is also required and a $200 transfer tax, plus a multiple month wait for BATF approval prior to taking possession for any individual owned full auto. Per Fed Law, all full autos must have been mfd prior to 1986 (almost certain of the date), so no new ones are available to individuals.
- LE agencies can purchase full auto on letterhead, but ownership and responsibility falls on the department.
- BATF reserves the right to inspect the storage and possession of any full auto guns at any time. So, yes you do give up your right to searching your home without a warrant if you own full auto and store them in your home. The likelihood of the BATF marching on someone's house at midnight for shits and grins is nil, but if they are looking for something, you do give up some of your rights in order to be an owner of full auto.