Although not with a Luger, I know a rural farm fellow & family (good friends of mine) back in South Dakota that can put them in one hole all day long! Also, some years back, his son placed 5th in the Olympics in pistol shooting... collectively, they probably shoot a million round a year!!
But, it's all relative, given a big enough hole, I can do the same with some restrictions.. or conditions?
One, the hole has to be close enough...ideally, the muzzle protruding slightly thru the hole?
two, big enough, (see number one above?
three, no wind! Can't see when my eyes water...
four, group size, (what ever can be attained with one shot.... ?)
Reminds me of my fathers favorite drinking rules...
1) always cut me off at two, nawww, better make it two thirty!
2) the only two times I ever drink are alone or with somebody!
Best to all, til....lat'r....GT