Referenced product: UAMCX-5B-300-BLK-TAP
The MCX Rattler upper receiver does include the bolt carrier group. 

Referenced product: WRMCX-300B-16B-TFSAL-P
Hello and thank you for your service! We do apologize but we are unable to modify the rifle due to the liability (we don't do any gunsmithing or modify firearms). We are able to ship it to another FFL that ...

Referenced product: KIT-MCX-MAG-RELEASE
This is a replacement for the original / existing magazine release. It will not affect the insertion of the magazine (it will not lighten it).

Referenced product: WRMCX-16B-TAP-P
Response date: 9-24-18
We do have the FDE version in stock and have added it to our site: WRMCX-16B-TAP-P-FDE. It is worth noting that most APP MCX rifles are black and not grey (WRMCX-16B-TAP-P included).

Referenced product: CALX-MCX-9B-300-TAP
The kit does not require the op rod to be changed.

Referenced item: CALX-MCX-9B-300-TAP
That tapered ring sounds like the adapter for a non-tapered (non-Sig) suppressor or muzzle device.

Referenced product: CALX-MCX-6B-300-TAP
We believe the twist rate is 1 in 5 inches.

Referenced product: HGRD-MCX-CARBINE-BLK
This is for the original MCX (not Virtus).

Referenced product: HGRD-MCX-CARBINE-MLOK-SD-FDE
This is a VIRTUS handguard. If the part number includes -MLOK it indicates VIRTUS.

Referenced product: BAG-MPX-DEPLOY-TAN-2
The Rattler will fit in this bag: