BudsGunShop.com - Caliber size

Yes and yes.

5.56/.223 and firing pin included.

I put this in my last .223/5.56 build and it works like a charm and cleans up easily. Be sure to check the headspace after you install it.

Yes to 5.56 or .223 and firing pin included.

Yes, it has a firing pin, and it can be used for 5.56 and 300 Blackout.
It's ready to go as is.

Bolt - Carpenter 158 heat-treated, shot-peened and magnetic particle inspected.  Engineered from  government drawings for NiB-X. Milspec gas rings. NiB-X coated (40% more wear-resistant than chrome).
Extractor - Manufactured, heat-treated, and hardened per government drawings.  NiB-X coated.
Firing Pin - Manufactured, heat-treated, hardened, chromed and certified per Government drawings.
Carrier - M4/16 style full auto (heavier) functions in AR15 and M4/16 platforms, 8620 material, heat treated and case hardened. Manufacturing tolerances and surface finishes tightly controlled. NiB-X coated for durability and ease of cleaning.
Gas Key - Hardened to USGI specifications and attached using grade 8 hardened fasteners.  Permatex No. 3D Aviation Form a gasket Type III Sealing Compound per MIL-S-45180 used on assembly. NiB-X coated. Staked per military specifications.
Cam Pin - Manufactured, heat treated, hardened and certified per government drawings. NiB-X Coated.

Yes