3 year Study results of QCB Upper & Grendel

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I doubt the LMT would do the same thing, since it locks up in a totally different manner, and many people report great accuracy with the MWS. The MWS pinches the barrel extesnion with a cross bolt torqued to a certain ft-loading, with another turn-bolt to secure the barrel extension flange.

I will also reiterate that I have the Gen I MGI QCB upper, which I purchased used from a guy who was into NFA stuff, and ran a lot of 9mm suppressed through it. He needed cash for another happy switch blaster, and sold it to me.

The MGI QCB has two vertical locking channels that have less than half of a circle on them. These internal faces rotate against a standard AR15 barrel's extension flange, holding the barrel in-place against the upper. I'm not sure they have anywhere near the foot-pound loading of a conventional barrel nut torqued to 35+ft-lbs. I had really tight vertical spread, but really wide horizontal spread.

I still love the MGI QCB upper, for a convenient little package that can be broken down smaller than a regular AR and fit into smaller cases. It would still be minute-of-badguy out to 300yds, but I'm an accuracy nazi who expects to be able to shoot sub-MOA if the barrel can deliver it, and that is what I wanted to know about this barrel.

Well I definitely thank you for the info. I have been pondering over one for a long time. The briefcase picture was pretty tempting. I have one of their modular lowers for my Shrike, and I started to order their upper a couple of times. The price and lack of good reliable info held me back. I take your reviews seriously.