The jury consisting of Tazo Kobayashi, Bosguerrilla and the editorial staff of HyperDouraku have awarded the "custom of the year 2019" prize to such a thing:

It is a gas-powered replica built on the basis of the GBB mechanism from the S&T M4 carbine. Here is a video presenting the operation of the replica:

And the second one which clearly shows its design:

Several other awarded inventions in the order given by the competition's organizer.

Owen - replica of an Australian submachine gun (GBB):

The mechanism used was taken out of a Colt 1911 - GM7.5 Tanio Koba replica. Other parts are 3D printed.

A cross-section (model) of the IWI Desert Eagle pistol based on the Hudson Desert Eagle .44 HW replica.

What is this for? It is very easy:

In our opinion, the most interesting - Automat Nikonowa - a fully working AN-94 EBB replica

Built based on the basis of an M14 replica mechanism (V7 gearbox).

A video presenting  it in action:

And finally, a "cartoony" replica based on the Tokyo Marui Thompson SMG:

Source: HyperDouraku