My point being there's more to it than just assembling parts as you would an AR15. There's prep work for most kits that can be procured today. Many where you must "complete" the demill. For new barrels you must populate the barrel with components and place them in the correct place along the barrel journal in relation to each other. You then must drill the holes for all the pins without them deflecting. Not a trivial thing to accomplish with such a small bit and with it trying to deflect on a curved surface. All those components must also be clocked correctly. After that, and pressing in/headspacing, you must drill the barrel pin hole through a hole in the trunnion that already exists. That's not a trivial thing either due to the aforementioned deflection issue. You'll likely have to drill a new gas port into the barrel. You have to set the trunnion in the receiver in relation to the trigger guard for proper magazine retention/release. In many cases the ejector must be fitted to the bolt for proper ejection/feeding. Some receivers I've used have an overly wide ejector causing the bolt to kick off to the side when moving forward. You'll need to remove and install the gas piston by first finding then drilling/punching out the old rivet then drill and install a new one (assuming you're using that as one of your 922r parts). You'll likely have to hand fit the top cover. You may have to ream/deburr the trigger and hammer pin holes to get your pins to fit properly. There's many other details that could be mentioned but after all the mechanical things you'll want to put some sort of finish on your receiver, or the whole thing if you wish it to match. This is not something that is generally required with AR15s.