My reply was sent several days ago now.
I'm still a one man band, time on the PC is time away from production.
One-off builds do not get the advantage of CNC so have to be done on the manual lathe.
If you enlarge the image enough any thread will look rough.
For the record, a 1/2-28 thread will never work for mounting a suppressor to a .45 barrel, ever.
.578-28 is the industry standard.
I suppose I need to add more detail to my site, I've been trying to keep it lean.
From my FAQ, http://www.specialinterestarms.com/index.php?page=faq
How do I get my old barrel off? It's REALLY stuck!
Seven out of ten Enfield barrels are extremely hard to remove, we find that the easiest way to get them off the action is as follows. If you do not have a lathe, a local machine shop or gunsmith can handle this for you at a nominal cost.
A. Strip the action of the stock, rear sight, and all small parts which might come loose while the action is spinning in a lathe.
B. Strip the bolt assembly, you will need a firing pin removal tool.
C. Insert the bolt body into the barreled action.
D. Mount the barreled action in a lathe with a "swing" of 9" or larger.
E. At the receiver end place the firing pin hole in the bolt body on a live center mounted in the tail stock.
F. Chuck the barrel in a self centering three jaw chuck.
G. At very low speed turn-off the barrel shoulder (Chamber area just in front of the receiver) to 1" diameter using a thin blade parting tool. Wear safety glasses!
H. This will relieve pressure on the barrel shoulder and threads, the barrel should now unscrew easily.
Since the barrel shoulder has been machined back the barrel is now scrap, and will never be usable in .303 again.