Picked up a Mac-10 at auction (Collar City).
Not normally a Mac fan but, I saw this priced right, and I had had a feeling it may be a preban being they designated it as a "M-10" not a M-11 which would typically indicate post ban mfg.
New mfg Macs are like $300-400. Prebans bring $500-700. Open Bolt prebans are $1100-1300.
Details of gun:
9mm, preban, open bolt operation (1981-1982 mfg). No magazine came with it, so ill need to hunt for a few but..
Here it is.