Ok here we go.
Got Phantom lined up on barrel, in place with crush washer and marked Phantom. Drilled 3/32" hole and countersank start of hole. Measured and drilled into barrel (Go SLOW HERE, very easy to drill into bore), measured and cut 3/32" roll pin to length and installed. Pin stopped just below surface of Phantom, bottom of countersank area.
Next, up to the shop for the Mig Welder to spot and fill the countersank hole up permanently.
Next to file down the spot weld and apply some type of finish. Just a rough in for now cauze I want to shoot the thing today.
Then, mount barrel to new CMT upper (with feed ramp cuts) assemble all parts etc.
Notes: I did the drilling with a cordless hand drill.
It would be very easy to mess up a barrel. And thank God I can weld.
The Colt 14.5" M-4 barrel came from Eagle Firearms and is advertised as "Like New", Looked New to me. Not a scratch or blemish on it, very nice.
CMT flat top upper from Denny, has M-4 feedramps to match barrrel extension.
Goes to show it can be done by the average Joe who is somewhat mechanically inclined.
This is something that you should not attempt in a hurry, or if easily distracted IMO.
YMMV, IMO, IMHO, HTH.
Danny