For my lower builds I generally assemble my own kits of known quality. They aren’t the cheapest option, but I know they’re safe, reliable and top shelf quality.
Pistol grip: Whatever your preference, the default for me is the rubberized Magpul MOE grip.
Pistol grip Screw: V7 Weapon Systems titanium grip screw
Receiver Extension: V7 Weapon Systems 2055 lithium aluminum receiver extension. The lightest, toughest extension you can get. The extension offers a significant number of stock positions over the typical extension. If using a stock that doesn’t require a carbine receiver extension, plan accordingly.
Receiver plate: V7 Weapon Systems aluminum receiver plate.
Buffer: JP Enterprises Gen 2 Silent Buffer with extra spring pack.
Buffer Retainer: V7 Weapon Systems titanium retainer, comes with the spring. I install these even with the JP silent buffer since I don’t like the buffer just falling out.
Trigger Pack: Geissele all the things, whatever flavor desired.
Trigger pins: Use the Geissele or if you’re chasing lightweight, throw in a set of V7 Weapon Systems titanium pins spec’ed for the Geissele trigger.
Bolt Release: V7 Weapon Systems S7 steel bolt release with spring, plunger and pin. Or the Battle Arms Development billet bolt release. Both are nice and will beat any MIM parts any day of the week. This is particularly important in pistol caliber builds.
Takedown pins: Battle Arms Development enhanced pins. Titanium if you’re chasing lightweight. These will come with the detents and springs.
Magazine release button: V7 Weapon Systems makes a nice button. This should come with the spring.
Magazine release catch: Norgon Ambidextrous releases are the best out there if applicable to your lower.
Selector: Battle Arms Development CASS Short Throw selector. Long/Short thin levers. This will come with a quality selector spring and detent. Depending on your lower, you may have to file down the lawyer pin on the selector core to get it to fit in to your receiver. The CASS is a better design if the ASS.
Trigger guard: If applicable to your lower, I’m partial to the Magpul enhanced trigger guards pattern.