I have a pre-ban upper (no bayo lug, once had flash hider and the complementary threaded muzzle.)
 
I want to make my rifle a legal postban. I do not want to purchase any other uppers or lowers for now, so please do not suggest this.
 
I have removed the flash hider. I then filed down the threads to smooth metal and blued the end of the barrel.
 
QUESTION:

What difference in accuracy can I expect from my rifle now with it's thinner muzzle section...
 
...and...
 
...the very same rifle above with the thinner section cut off and the new muzzle re-crowned by a qualified gunsmith.
 
Pay the extra bucks or leave it as is?
Advice?


 

You shouldn't have any measurable effect on accuracy with your barrel as it is now. You don't mention how long your barrel is but if it's 16" it will be illegal (a Short Barreled Rifle, SBR) to shorten it anymore. If it's a 20" shouldn't be any problem to cut and recrown.

I'd also suggest you post questions like these in the "Build it yourself" area.

If it were me, I would have left the threads alone, and screwed on a nice muzzle brake, then TIG welded it...
Since the threads are already toast, To make it look like a clean job, I would remove the barrel from the upper, place it in a lathe, and cut down the end of the barrel and crown it...(assuming the length is over 16")
If cutting the end of the barrel makes it too short, then you could press-on a custom muzzle brake,(bringing it over 16") and TIG it in place to make it permanent...AND LEGAL.
 

Just my $.02