The 'non-shooters' the other guys are referring too are called MMG and are dewat Machineguns... Completely legal in almost every part of the world...except the USA....the receiver is real, hardened, has three pin holes, complete fire control group,
and is ready to go with a new trunion, barrel and bolt/carrier. This one on ebay is NOT an MMG.
Not sure which 'extra' hole you are refering to, but the Junker 1 has no trigger group axis pin holes drilled into it. The Junker 2 and 3 have the semi-auto holes drilled, and not the trip sear hole. So they are basically semi auto shells that need proper rails and a good heat treat. Of course trunions and all that other jazz too... Some clown on DOT.NUTZ built one on a Junker 3 and advertised it to everyone, leading to them being put on the gov't do not allow for import list... I can totally see the MMGs being a nono, as once a MG always an MG...the receiver is what counts.
But the Junker 2 and 3 are much farther away from being an operable firearm, and certainly cannot be considered MGs no matter what law you twist. The Junker 1 however, was the one named on the ban list, and Ironically, it is the one most closely akin to a simple toy.
Where as one could 'theoretically' convert a Junker 3 into a rifle, the Junker 1 is a complete waste of time as the whole bottom is cut out to fit the air pistol. SO yes, the receiver is junk as far as the Junker 1 is concerned... Trunion, absolutely useless.
Bolt carrier cut to shreds to accomodate the pistol. barrel is demilled or unfinished...in the case of the Junker 1, the cleaning rod is the barrel! At least the Junker 2 and 3 have a 4.5 mm barrel that the BBs come out of. Gas block, press welded on, not pinned so it can't be resused easily...even if it could, the gas chamber is not finished reamed or chrome lined.
No bayo lug. FSB is modified to accept the cleaning rod barrel. Again, it is press welded in place. So is the rear site base.
The plastic stock is cut to shreds on the inside, and there is a plug on the rear screw area. Trigger gaurd is GONE, mag catch useless except for the catch/spring itself.
SO, for $450 you get a gas tube, an upper and lower handgaurd (which the lower is cut up and missing the heat shield to fit the 'barrel'),
a top cover, recoil spring, and a rear site leaf. Oh and a pretty poor example of an air pistol to plink cans with. The Junker 3 list is quite a bit better than that, making them worth a $450 asking price, but they are scarce now. Hope this answers your questions-
-C