The Wiki says: The .223 Wylde is a proprietary rifle cartridge chamber with the external dimensions and lead angle as found in the military 5.56×45mm NATO cartridge and the 0.2240 inch freebore diameter as found in the civilian SAAMI .223 Remington cartridge. Rifles with a .223 Wylde chamber will typically accept both .223 Remington and externally slightly larger 5.56×45mm NATO ammunition. The .223 Wylde hybrid chamber was designed by Bill Wylde of Greenup, IL to exploit the accuracy advantages of the .223 Remington chambering without pressure problems or compromising the functional reliability of (semi) automatic weapons like the AR-15 family when using 5.56×45mm NATO military ammunition. Coincidentally, it shoots the relatively long and heavy 80-grain (5.18 g) bullets commonly used in the sport of Highpower Rifle Competition very well and is one of the preferred chambers for that use. The Wylde chamber is used by a few rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels, and upper receivers.
Not bad, but the twist has more to do with the accuracy of the heavies. Yes, you can shoot .223 Rem and 5.56 Nato from the Wylde chamber.
Lower Choice: You want a lower that is know to be dimensionally correct, there are two types of aluminum, does not matter much, but a good hardcoat anodizing is important. Other than that, it is all fanboy, aesthetics. I have LAR, JP, Lancer, Seekins, Firebird, Tactical Machining, Del-Ton, Stag, SunDevil, Cav Arms and Mag. The polymers are not worth it unless you are building an uber lite or a dedicated .22LR. Even then only a Cav Arms or a GWACS. Seen to many extension tube and buffer retainer area cracks to trust them. I tried a Mag, no-go for me.
The right side bolt release through the lower is a cool feature (Lancer and Seekins) as I am not a fan of the bolt release in the trigger guard. No actual relationship to accuracy. However, if the upper to lower moves, that relationship is off, but scope is on the upper. Also, some lowers (like Seekins, Firebird) have the screw to tighten the connection and adjust overtravel of mil-spec triggers. Unless the features of the Seekins or Lancer really appeal, go with a stripped lower that has a decent rep and you will be fine.
The lower is easy to build and you don't need any special tools...but roll pin starters/holders are really nice. Watch 3 or so of the videos and get to work.
Trigger is subjective...I don't like 2 stage and the Geissele's never appealed to me. In the single stage, POF is bomb-proof and good, if not a tad heavy. CMCs and Jards live in most of my ARs. I have 2 JPs, and they are great, but they are also a total rebuild at maybe 10K or so. Triggers don't affect mechanical accuracy at all. But a lighter trigger does help cover some sloppy trigger control.
Upper...a quality receiver is huge. I will only use JP and Seekins. The bore at the extension is small enough that there is a tight or even interference fit with a mil-spec extension. This is huge for accuracy, as is properly seating the barrel, a trued interface and multiple torques to burnish/seat the threads using anti-seize. Other than the barrel, that is where ALL the accuracy comes from.
