Hello from Poland, folks
Just bought myself a new MCX Virtus, took it to the range, shot a hundred rounds and then noticed that there is a fair amount of play between the upper and the lower, and it’s definitely worse than my other ARs. Is there a cure? I’ve heard about Accu Wedge for AR15 lowers, but there is a factory one already inside my Virtus (not doing its’ job though). How do you tighten it? I’ve checked inside the pistol grip and there is a screw there but it seems to be the one holding the grip itself.

P.S. I do like this carbine a lot, it’s just this sloppiness between upper and lower on a new firearm which irritates me the most.

I don't like rifles that flop around like a rag doll either and have eliminated it with mine by various methods.
Your lower receiver is drilled and tapped for a tension screw, they used to come with a spring loaded one that was accessible with the grip removed.

One like this is adjustable after the screw and grip is installed.
You can get nylon tipped ones also like the ones used in Aero Precision lower receiver's.
https://www.armorydynamics.com...sion-Screw_p_30.html

And by the way, welcome!! Your name caught my eye, somehow. Americans love Poles, and I think it's mutual based on my visit there in 1990 and Poland's policies since then. Poland is our best ally in Europe, IMO.