A couple of things to keep in mind: 10/100,000. As in if it is an ILLEGAL, NON-REGISTERED machine gun, you get 10 years in a Federal Pen and a $100,000 fine.
Now: Once a Machine Gun always a machine gun. If I take a registered Receiver M-16 and convert it to semi-automatic only, it is STILL an M-16 in the eyes of the ATF and has to go through all the transfer paperwork, transfer tax, etc.
There is no-such thing as a Semi-Auto MP-5. The Civilian legal versions from HK have 16" barrels and are called the HK 94 and the SP-89. The SP-89 is a pistol version (in full auto trim, it is called the MP-5K).
If the gun has: less than a 16" barrel, a "push-pin" lower (takes full auto lowers direct from HK with no modifications), a folding stock on an SP-89, it is illegal, unless it is a registered Machine Gun or Short Barreled rifle.
If a Machine gun is not "papered", it CANNOT be reigstered or made transferable.
The only "Semi-Auto" MP-5's are FBI guns--they are machine guns with a special order semi-auto lower, but could be made into full auto by swapping a different lower on to them. They are still regulated and registered just like full auto machine guns, and are all "post samples".
There are 3 statuses of machine guns in this country:
Transferable--imported before 1968, or domestically made before May 1986 ("domestically made" also includes most of the MP-5's in the country--they were imported guns that were converted to machine guns in one of several ways--they are still considered domestic manufacture).
Pre-May Dealer Samples--Only a Class 3 dealer (currently or has given up his license) can posess these. They are the imports from 1968 to 1986. A dealer may retain these once he gives up his license, but can only sell them to a dealer (they never become transferable).
Post-May Dealer Samples--these are all MG's imported or domestically made after May 1986. A Dealer may have these, but must have a "demo" letter from a LE agency to have them in stock.
To give you an idea of the prices:
Transferable MP-5's (all converted Semi-auto Guns) are $7500.
Pre-May Samples are $5000 (still expensive, but the dealers pay it because they can keep it when they give up their licenses).
Post-May Samples are $1200--this is what the Police get.
Conversion of Semi-Auto HK's WERE (no new production of MG's for civilian sale since 1986, remember) done by Registering the reciever, and converting it to a Push Pin (making it identical to a factory gun), Registering the reciever and using modified lowers (the lower must be kept with the gun, or it becomes an illegal conversion part--since the reciever is the registered part, but the lower is modified), putting a Sear (the registered part) into the gun, or putting a Trigger Pack (a registered part) into the gun.
It is vaguely possible that the gun was a sear host (the sear is the registered part), and once the sear was removed, the gun would be semi-auto again. However, if the barrel is under 16" total length, it would be illegal unless it was registered as a Short Barrel Rifle.
What you might be thinking about is an HK 94, the semi version of the MP-5, and that is legal as long as the barrel (and permanant attachements) length is over 16".
How much is it to be sold for? That would probably give an indication of what it is.
AFARR