I had to stop working on the 3D printed M56A2 for now,
but I can tell it is so light that I will upgrade/reinforce it with metal and would still be able to carry it the whole day.
For the real deal full metal replica well, you have to get used to it to carry it for longer than an hour.
With proper training and the right arm and _vest_ you can do this like the whole day if you're fit enough.
For me the tricky part is how good you are carrying it when it comes to corners, stair ways, elevators etc. at Cons.
We once did a fun training exercise video (running, jumping and all the fun stuff) about 15 minutes, don't ask if the vest had a "certain" smell.
But it all was possible with the 12kg setup.